There are plenty of lesser-priced third-party 28's out there, most are at least decent, so if budget is a consideration, you won't go too far wrong with any. And you should be able to find them in K-A mount. Vivitar, Soligor, Focal, and on and on, there's loads of them out there. Keh seems to sell these as 'miscellaneous' brand, ie. they don't differentiate among 28/2.8's.
For 24mm, especially if you already have the Adaptall K or KA, the 01b/01bb Tamron is pretty nice (KEH sells them for a bit over $100 new). The problem is the cost of the adapter, especially the KA.
If you luck out you might find a smc-a 28/2.8 pentax - I like mine and it sure is easier to use on digital than a M lens. I found mine at a great price since it was attached to a Program Plus camera