Check this out:
h**p://www.ucos-ii.com/ports_v1.htm
* -> t
This is the author's homepage. The 8051 port should be free to download. However, if you want to use it for commerical purpose, you might have to pay a fee.
When Intel moved on from 8051 RUPI44 etc they released DCM51 to the public with all source as well, though designed for PLM51 it works well with K*e*i*l, you may have to dig deep to find it, f/i/l/e/s/e/a/r/c/h/./r/u/ is a good place to start..