There are pics of Su-30s in russian colors with bort numbers 388/389 (visited paris and singapore air shows). Eg 388...
The 388 is in fact a stock Su-27 (look at the picture of your link) and the 389 was a Su-27UB. Don't forget about the existance of the twin seat trainer
Also 501 & 502 pics are also pretty common but not sure if these remain in Russian service. Understand 503 and 504 were delivered to China.
The 500 series were in fact Su-30MKK prototypes/pre-production aircraft. Some of these aircraft are still flying for Sukhoi and were used as Su-30MK2 test beds. The 503 was in fact not delivered to China but is currently used for testing the Irbis radar for the new Su-35.
There is also a pic of the Su-30KN with 302 (c/n 1010302). This could have gone to the IAF...
The board number 302 was the Su-30KN prototype built from RuAF board number 53. The RuAF originally planned to upgrade their dirty hand full to that standard along with some Su-27UB, but eventually decided to go for the Su-27SM upgrade. I don't know about the status of the 302, but it was definitely not delivered to India.
btw, you'll get to see a lot of 01-06, 597/603 pics as well (these are of course 51-56 series).
The 01 & 06 were the first Su-30MKI prototypes. The 01 was in fact converted from the RuAF board number 56. Sukhoi additionally built the Su-30MKI pre-production aircraft 04 & 05 which are now used as testbeds for the Su-30MKM & MKA.
The 603 was the original Su-30MK demonstrator and was converted from one of the 2 Su-30 prototypes, which were built in the late 80's.
The 597 was one of 2 Su-30 preproduction examples which passed the flight acceptance tests and was handed over to the Test Pilot Aerobatics Team of Anatoly Kvotchur after completing their tests. I'm not completely sure if the second example was handed over as well as 596 or 598, but I mean to remember both aircraft were delivered to the Aerobatics Team.
There is also this interesting pic of a 67 in 2006...
That is indeed the only board number I don't know about. It seems to be a Russian Knights aircraft. Might be that this is the former 302 or one of the Test Pilot Aerobatics Team examples decribed above.
greets Scorpion