Hi Andrew,
I am not sure that a shallow draft keel or bilge keel boat is better for junk rig. I think it is more an attitude of mind of those who choose junk rig. Junk rig lends itself to easy handling and reefing and more relaxed sailing. A shallow or bilge keel boat allows the crew to take advantage of shallower more protected anchorages and with bilge keels the opportunity to dry out level at low tide and even walk ashore. Deep fin keels, on the other hand, mean that you need to anchor in deeper water and are more exposed to the weather, you also need to get the dinghy out and row ashore. If you accidentally go aground with a deep keel boat she will dry out on her side and be very uncomfortable if not impossible to stay aboard, unlike a bilge keel boat. Shallower keels tend to be less able when going to windward, this is also the weak point of the junk rig, so having a shallow draft or bilge keel boat with junk rig means the performance to windward will be less than a high performance bermudan rig with a deep fin keel, however most junk rig sailors are prepared to accept this compromise for the advantages of the shallower keel and the junk rig.
All the best in your search for a boat.
David.