Places have AVR USB Boards still in stock
Since the PIC chip won't be easy to flash,
You can order the Teensy from here
USBTiny MKii from US
this one use ATmega32U2 and compatible with psgroove, US
it has the design similar to the ATAVRXPLAIN, but use a different AVR USB chip.
So ref to the sticky thread on how to flash, but remember to use the ATmega32U2 hex file from the hex thread.
Olimex AVR-USB-162 France
Open Kubus USB-Stick (AT90 USB) Germany
AT90USB162 USB Board (Olimex AVR-USB-162) new stock
microcontrollershop.com has the Olimex AVR-USB-162 board back in stock: