Hard question to answer. Only side mount I know for the mosin nagant is the repro sniper mount (which works well if you ask me).
Other problem is that you probably don't want to consider ever reselling that gun if you get it scoped and permanently altered. Polish M44's in good condition are worth a lot, but if you scope it, kiss that value good bye.
Good scopes for mosins that aren't side mounts are the scout mounts that go on the rear sight. In a carbine like the m44 it's particularly suitable because of the recoil and muzzle flash.