My guess is you need the Weaver #2 Side mount - Weaver part # 48402. You will also need side mount rings such as Weaver part #49350.
At the Weaver site you can find these at this link:
http://www.weaver-mounts.com/product...eTopMount.aspx
If you download the catalogue you can find the models which fit. Here are some photos from a US site. You can get the rings and base at Wholesale Sports in Edmonton. $32 for the rings, and $16 for the base. Then of course you need a 1" dia scope. They have a web site.
http://www.midwayusa.com/eproductpag...eitemid=272671
http://www.midwayusa.com/eproductpag...eitemid=119028
http://www.wholesalesports.com/onlin...category=10300
This said, I recall my father having this style of mount which used the smaller .22 size sope. Didn't see these in my quick look.
Ron