No I don't, but it has been a pretty long time - longer than the span between the first two. I don't think they were very popular. Although I'm not really a big fan of westerns, I thought they were pretty good. Some closure to the story would be nice, though. I hate books without endings.
The original contract called for three books, probably based on sales. Boxleitner had the third book half written when it was cancelled by the publishers.
He is now trying to shop the three books either as a movie or a miniseries (according to comments he made at one of the cons.)
Judging by the results of Firefly, I don't believe a Western/Scifi mix works with the general public.