Actually, most 30's and 40's rimfire scopes were 3/4" tubes. There are usually tons of old Weavers on eBay and usually go for reasonable money. 7/8" rings are hard to come by, but the 3/4" are still readily available from most makes. Even an inexpensive Bushnell 1 1/2-4 1/4 like this would serve you quite well.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3658688549&category=31716
