Burris and Tasco make inexpensive rimfire scopes with 3/4" tubes, but I can't vouch for their reliability. Redfield used to make a nice one that you might find listed on e-bay.
Interesting pattern on those critters, very different looking from eastern tree squirrels. Sounds like you had some tough odds working against you. To spite it all, ya still scored!!!
Very sweet looking 39. Congratulations!