A lot of the “better” EU plums are grown in france 
and also netherlands
So me and @mrsg47 are lucky that way 
Reine Claude Verte (likely the oldest green gage known)
One of if not the oldest green gauge know is likely the Reine Claude Verte. (we often cal it RCV)
Some sources say Reine Claude Doree is the same. Some note small differences.
Almost all literature says Reine Claude Verte to be “superior” to all other plums.
Although tastes differ ofc.
They do however are hard tree’s to get producing. And have relativly small fruit (30 gram 32-42mm are noted in some sources)
They seem to get more productive when own rooted. And they readily root on their own. (when rivers flooded plum orchards in the winter, all RCV rooted on branches)
See the green gage sources below.
If it’s for own use. Id say “search for a Reine Claude Verte or Reine Claude D’Oree (doree)”
For more reliable production some more comercial plums similair are
Reine Claude d’Althann
Reine Claude d’Oullins
Mirrabelle plums might also be intresting.
Mirrabelle de nancy comes to mind. It has small plums though. Roughly 12grams or half greengage.
Bellamira is a modern larger version. roughly twice the weight.
other intresting eu plums
Opal is another plum thats highly popular here. And it is really tasty and early season.
Belle de thuin might also be intresting. It’s really large. roughly 3 green gages in weight.
Czar or (the Czar) is know for being a really strong plum. So if your growing conditions are challanging for EU plums it might be worth a shot.
I have little experiance with japanse plums. So you’ll have to look to some one else for advise on those.
If there is little know/experiance with plums in your region.
Id recomend a shotgun approach and just try out a lot of different plums from different “groups”
Sources/links/further reading (use google translate)
Lots of dutch info/research on plums and gagues
ill post some links in the rest of this post. Those are mainly in dutch (due to extensive growing of green gauges in the netherlands a lot of research and writing has been done on them and other plums)
google translate
You can use google translate to translate. Translation to english i checked and looks really good. If in doubt about the translation of a specific word or thing. You can ask me to have a look and translate
I explained in this post how you can get google translate to work. I especially like the chrome plugin.
extreemly extensive source on everything green gauges
https://www.vriendenvanhetoudefruit.nl/wp-content/pruimen/reine_claudes.htm
Extreemly extensive source on “all” other plums and types of plums
https://www.vriendenvanhetoudefruit.nl/wp-content/pruimen/
if you clink on the links on the page you get more information.
Like on mirrabelle plums you get
https://www.vriendenvanhetoudefruit.nl/wp-content/pruimen/mirabellen.htm
https://www.fruitlent.nl/reine-claude-verte/
https://library.wur.nl/speccol/fruithof/fruit/Pru/Tekst/PruT10.htm
https://library.wur.nl/speccol/fruithof/fruit/Pru/Tekst/PruT08.htm
https://library.wur.nl/speccol/fruithof/fruit/Pru/Tekst/PruT09.htm
https://www.fruitlent.nl/reine-claude-doullins/
https://www.fruitlent.nl/bellamira/
https://www.fruitlent.nl/opal/
https://www.fruitlent.nl/belle-de-thuin-rgf/
reine claude de brahy and bravy
https://edepot.wur.nl/412447
This source might intrest you if your looking for a specific trait or reference
page 21 are the plums. (there are also pages for other members of the prunus family)
You might also want to look into plum rootstocks
I think the netherlands actually exports a lot of rootstocks to india.
Some rootstocks for sale here are
-Sint julian A. Quite large. but really strong. Can root sucker
-Sint julian “wangenheim” A seedling from controlled pollinated seed sourche. No suckering problems. Is also used in germany. And is slightly smaller then Sint julian A. Some variability is still there due to it being seedlings. There are tissue cultured selected clones of wangenheim.
-wavvit
-weiwa
Wur S766 Prunus spinosa. Is a verry intresting new rootstock. That seems adapted to many soils.
VVA-1 = KRYMSK 1 – *Prunus tomentosa x P. ceracifera *
VSV-1 = KRYMSK 2 – Prunus incana x P. tomentosa
https://p2g.us.com/index.php/krymsk1/
https://www.janssen-rootstocks.nl/uploads/EFM%20Artikel%20NL.pdf
I have heard some anecdotal disease problems about the krymsk series.
For larger tree’s id go for Sint julian A
For smaller tree’s id go Wur 766 or wangenheim or their in vitro selected clones wavvit and weiwa