Performance Bicycle (performancebike.com) has a seatpost rack with pannier mounts. It is their item number 00-0041D, and is on offer this month for $34.99. I am not on their payroll, honest! (I just placed an order for a few other items, including a rack duffel, and I recalled seeing the rack.)
As for using a rear rack on a frame with no dropout-level eyelets, try this: All frame racks come with two plastic-coated metal clamps that you can use to attach the rack to the top of the seatstays in the event that your bike has no high-level eyelets (and most do not.)
If you purchase such a rack, you can obtain a second pair of those clamps, and attach the bottom of the rack to the bottoms of the seatstays in the same manner as the tops.
You can take the supplied metal clamps to your LBS, and see if they have any spares they can give... or sell to you. Also, check out the "Nut & Bolt" supply stores... the ones that cater to commercial and industrial customers... I've found such clamps in various sizes... for mounting conduit, I believe, in Nut & Bolt suppliers.