I am afraid I don't fully understand your question - what kind of board are you looking for? A board with a socket for the microcontroller and headers to connect to the port pins?

BTW, just a word of warning - make sure whatever pre-made board you get can put your DS89C420 into ISP mode. I don't think the required conditions are standardized, using the DS89C420 and P89C51RD2 as an example:

DS89C420 must be HELD in these conditions during ISP mode:
RESET = 1
PSEN = 0
EA = 0
RD = 1 (This is errata for Rev.2!)

P89C51 must meet these conditions on the falling edge of reset pulse to enter ISP mode:
PSEN = 0
EA = 1

Hope this sidenote helps.

- Lee Cross