Most red dot scopes come with Weaver mounts, and therefore will fit the 22A. However, and this is a big however, *some* of them will not fit. It depends on the spacing of the crossbolts in the mounts. For instance, the Simmons 40mm has a one-piece mounting rail that has crossbolts that slide along cutouts in the rail. The 22A has gaps in the spacing of the crossbolt cutouts in the rail, but no matter where you position the crossbolts in the scope's mount, one cannot get the bolts to match up to the pistol's cutouts, no matter where along the rail you position the scope.
Here is a link to the type of scope that I'm referring to:
This doesn't happen with most pistols, but because of the gaps in the 22A's cutouts, you will want to find the red-dots that use separate ring mounts at each end of the tube. This type of mount will give you more options for positioning of the mounts. Here is a link to an example of this type:
As you can see, this type uses a smaller diameter tube to accomodate normal ring mounts. I've used this type (not this brand) on my 22A without any problems. If I get a chance, I'll put up a pic later....