Hi again,  I have been Google-ing thru the internet and via c4dcafe.com found some free mirror-ball style HDRI probe images which should work in Bryce, some are better than others:

http://www.deviantart.com/deviation/25795163/
http://www.deviantart.com/deviation/10152791/
http://www.deviantart.com/deviation/10036562/
http://www.deviantart.com/deviation/9597501/
http://www.cgmill.com/olmirad/hdr.html
http://www.bencloward.com/textures_extra.shtml