www.maxobjects.com will turn up the authors of most Third Party Objects.
Seqplayer was written by Eric Singer, I ported the original code to Intel Mac UB and I recall that someone else used that to build a Windows version. The link should be at Eric's site (which you can find through MaxObjects).
Lsymcat sounds like one of Peter Elsea's LObjects. If it's not listed at maxobjects, then search on LObjects, which I *know* is there.