The SU Match EXTRA ammo is around in Germany, but not wholesale anymore, some dealers may have some boxes, but that's it.
Ammo for the 6,5x54R is even harder to get, I know a dealer, who has such a rifle in his collection and some ammo too, but he does not sell any.
Only way is relaoding for both types. For the 7,62mm cartridge use Lapua D166 bullets with 45...46grn N140 at an OAL of 76mm.
For the 6,5mm Lee may make some custom dies and than you can start with the data for the 6,5x55 swedish.
All the russian match ammo was made by LVE Novosibirsk factorycode 188.
This is my rifle.
I have many like it, and they are all MINE.
My rifles are my life. Without my rifles I am useless.
I must buy any cheap Milsurp, before Bubba does.
I will learn all about restoration and preservation of guns.
I must clean my rifles and shoot them often.
So be it, until all old military rifles have found a loving home.