Well, to alleviate this issue a little, I wrote a little mod that takes advantage of the new scripted spawning functions of the RandomSpawner:

Each weapon tier has two slots that can be adjusted to spawn only either one or two specific weapons from that tier (for example, adjusting the Chaingun options to Martyoshka and Power Overwhelming will only spawn those two particular weapons from that point on, and so on), or continue to spawn randomly chosen weapons like normal, so you can adjust your own specific little weapon loadout. Or heck, selecting one slot to (random) and the other to a specific weapon will cause the latter to spawn more frequently in that tier.
To run, just add this mod after Russian Overkill proper. The new loadout options menu should appear inside the "Real Soviet Stuff" menu. Note that "Class Restriction" in the Convienience menu must be disabled for this session.
Spoiler: Old version