The RX-888 adaptor kit is now available directly from TAPR:
If you are not familiar with TAPR, this brief introduction comes from their website:
TAPR is a non-profit 501(c)(3) organization of amateur radio (“ham”) operators who are interested in advancing the state of the radio art. The initials stand for “Tucson Amateur Packet Radio” but today the organization is much broader than that: we long ago became an international organization, and while we still support packet radio our areas of interest have expanded to include software defined radio, advanced digital modulation methods, and precise time and frequency measurement.
Turn Island Systems is proud to be associated with the good people of TAPR.