Dedicated .22 LR Rimfire Uppers for AR-Platform Rifles
A number of companies offer dedicated .22 LR rimfire uppers that work with any standard AR15-platform lower. Brownells carries dedicated .22 LR AR uppers starting at $419.99. Brownells offers flat-top AR uppers, allowing you to easily mount the aiming system (iron sights or optics) of your choice. Brownells offers a 100% satisfaction guarantee on all products it sells, including .22 LR uppers.

AR-Style .22LR Rimfire Rifles (Complete Guns)
Another option is to purchase a complete AR-style rimfire rifle chambered for the .22 LR cartridge. This option may be more affordable than you think. Right now Impact Guns is selling the Smith & Wesson M&P 15-22 with 16″ barrel for just $509.99 (marked down from $649.99). It’s a nice little rifle. The M&P 15-22 is designed and built as a true .22 LR semi-auto from the ground up, with ergonomics (and most operating controls) identical to a centerfire M&P 15 rifle. Here’s the black and tan version:

H&K offers the HK 416 D145RS, a dedicated .22 LR rimfire rifle. Engineered and built in Germany by Carl Walther, the HK 416 D145RS features a match-grade precision barrel, metal upper and lower receivers, retractable stock, and machined rail interface system with on-rail iron sights. These HK rimfire rifles (which employ a blow-back action) are accurate and reliable. Current ‘street price’ is around $660.00. One purchaser writes: “Great .22. I have had this gun a couple of months and have put about 500 rounds of 5 different brands of ammo through it. Not one FTE. I have shot other brands that can’t get through one 30-round mag without a failure. [The 416] is a little pricey compared to the competition but you get what you pay for.”