I looked into this topic a few months ago while preparing my route through Russia. There are actually more options than I expected, especially for longer trips between cities. One of the sites I checked had different vehicle types and booking dates available. You can see different car rental options in this country here https://getrentacar.com/en-US/russia

Road trips around Russia can take much more time than people initially think, especially if you plan to visit smaller towns. It is probably better to arrange the vehicle before arrival, because availability may change depending on the season and location.