Mud harbours are pretty standard in Europe, esp the UK. For that reason bilge keelers are much more popular over there than here, and easier to find.
But if you can find a Westerly or a Vivacity, they would fit the bill. There's always been a few of those around the PNW. I have seen boats with retractable struts that can be used to prop the boat up in a 'tripod' arrangement with two struts and the keel. Requires that the boat is happy to sit on her keel, of course. I suppose many smallish boats could be so modified or adapted.
An example of a bilge keeler:
Here's an article about 'drying out boats'
And here's another option: