Hans Summers (G0UPL) and Steve Farthing (G0XAR) have recently begun selling a new kit for a QRPp (150mW) beacon that can generate Hellschreiber, various QRSS modes and best of all WSPR. Unlike the ones now sitting unused in a drawer in G4ILO's shack which have my details programmed in, the Ultimate QRSS Transmitter Kit has a user interface with an LCD panel that allows you to input your own callsign, locator and power output. This means it has resale value - when you get bored you can sell it on and the new owner can program it with his own details.
I asked Hans if they were going to offer a version for 20m, which has become one of the most popular WSPR bands. His reply was that the kits will actually work fine on any frequency between 1MHz and 20MHz, they just require a different crystal and different components in the low pass filter.
A 20m beacon for WSPR would need a 14.097MHz crystal. I searched my junkbox and couldn't find one. Nor could I find a source for one and having one specially made would be expensive. Perhaps if there is enough demand for a 20m version it will be worth Hans and Steve's while to have a batch made which will be cheaper.