I don't sell camera tripods, but here is some information to help you choose one to buy:
First, you don't really need an expensive, heavy-duty tripod for Shamrock(tm) boxes because they are attached to, and are supported by the tripod's legs which afford a stronger, more stable support. The only thing the tripod head supports is the panel/canvas holder and the painting (about 2-3 lbs. total.)
The tripod should have standard-size legs, square or round...about 1"/25.4mm thick on the upper section works best. You might want legs with retractable spikes in the feet for outdoors, but this isn't required or necessary.
The tripod you buy should include a quick-release plate (most tripods do.) The quick-release is attached to the back of the panel/canvas holder for attaching to the tripod head. If you use your tripod for photography, also, it's convenient (but not required) to have two quick-releases...one to keep attached to the holder and one for your camera. Some tripods include two quick-releases or, if not, an extra one can be purchased.
I don't sell tripods but I'm including some suggestions. There are many good tripods that will work well with Shamrock boxes. IMO, three (not four) section legs are stronger and more stable. I recommend one of these SLIK tripods for a good, inexpensive choice. The U8000 is the same as the U9000 except doesn't have retractable foot spikes:
These Sunpak tripods will work, also.
(The SLIK has about a 36"-wide stance and the Sunpak has about a 28"-wide stance, at full leg extension.)