I don't think Mesa ever actually produced these as heads, but some people definitely loaded the chassis into head boxes, so some are on the market that way. I have a Studio .22 combo without EQ, and it's a great amp. One thing you should know about it, though, is that assuming it's not actually a .22+ version, you have no control over the volume of the lead mode relative to the rhythm mode. You will probably find that the lead mode is too quiet compared to the rhythm mode to be useful for footswitching between them without stopping to adjust the master volume. That's why they called it the 'Studio' .22--it was most useful in a studio setting where you could stop and adjust the amp to get different tones. There is a pretty easy mod you can do to add a separate Lead Master control, though.
These amps have a really sweet and rich clean tone, and a pretty distinctive lead tone that doesn't sound like other Mesa amps. I like it, especially with guitars that have single coil pickups. A good price for a Studio .22 combo in US dollars would be around $500, so a decent price for a head would be $350-$400.