ASDG's Art Dept. with Pro Conversion Pack does Pict conversion and about any
other format you can find. They have a section in AMIGAVENDOR forum. Also the
Video Toaster and ToasterLink can both convert PICT to IFF, although the
process is a bit convoluted (no pun intended).
The public domain software PBMplus will also convert to pict, I
believe, but you have to go IFF->PPM->PICT (i.e. you must convert to
PBM's format and then from that to PICT.)