Stanley Gibbons publishes a catalog that in non-COVID times can perhaps be found in your local library. If you are mainly concerned with the Soviet era and earlier, you can probably buy a gently used older edition for not a lot of money.
If you are still buying stamps from the US, you may need the numbers from the Scott catalog. Each volume is pretty heavy so shipping would be prohibitive even though a copy from a few years back would be inexpensive. There are those online that sell sections by country taken from Scott catalogs.
https://ufdc.ufl.edu/UF00020235/00119/citationMany back issues of the Rossica Society are now online. English language is used from about #44 onward.
Of course, you can ask questions here on SCF. There is a lot on Russia already archived on SCF.