Millet makes some very nice rings that fit the 11mm dovetail used on most rimfire rifles.
On my Marling 25MN (22 Mag) I have a 4-12X50mm Simons. Although an inexpesive Tasco will work fine. The more you can spend on scope the happier you will be. I had a $20 (on sale) 3-9x32 Bushnell on it orgianally and the step up in magnification and objective lens size makes a huge difference as the ranges get longer and light get dimmer. 4-12 is probably a bit overkill for a 22Mag but it does make it nice. The 50mm objective lens really gathers a lot of light which is nice in the early moring and late evening.
If I was putting together a 17HMR I would try to get at least 12 power if not 14. You want to be able to see those tiny little bullet holes at 100 yards.
Take a look at
http://www.natchezss.com/ they always seem to have pretty good deal going on scopes.
rambling
mcb