It is not easy at all to find stock oversized pistons for the Euro E28 535i M30B34 engine. Note that the piston in the picture you've posted is not for the E28 M30B34 engine, but for the E34 / E32 M30B35 engine. The correct piston for the Euro spec (10:1 compression) E28 has a piano-shaped top.
You may want to try Hubauer Shop in Germany, maybe you're lucky to still find them brand new:
https://www.hubauer-shop.de/en/
Before that, you may want to carefully double check the part numbers and make sure you're looking for the right piston. Realeom is very useful:
https://www.realoem.com/bmw/enUS/select
As a side note, you may use also the E34/E32 pistons, whose tops look like in the picture you posted. Despite that they yield a compression ratio of 9.0:1 in M30B35, when mated with the E28 M30 cylinder head they will get you around 9.8:1 compression. This is due to the fact that M30B34 combustion chamber volume is smaller than M30B35. Factor in the overbore, and you'll be very close to 10:1.
To make things even more complicated, note that there was also a super are 9.1:1 compression piston, unsed in the non-cat version of the Euro E32 735i and very late E24 635CSi. See the picture at the link below:
https://www.magicview.ro/mye28/pics/M30B35_pistons.jpg
For second-hand pistons, you may want to check:
https://www.kleinanzeigen.de/
As of now, there are several offers for used M30B35 (read E32/E34) "0" size pistons, none for M30B34 (= E28) Euro pistons, but one for "+25" (92.23mm) size M30B35 (= E32/E34) brand new Mahle pistons. Make sure you're seated before you read the price:
https://www.kleinanzeigen.de/s-anzeige/ ... 5-223-1857
Good luck!
