I remember asking this a while back and I think Ralph Lambrecht said to use Color Mount. I have the same problem as you. Just finishing a box of Buffermount. I thought it was pretty much the only archival drymount tissue left, but I find it quite finicky to use, and never really have confidence unless I leave the print in the press until the press cools - obviously not the way to be doing this if you've got more than one print to mount per day
I didn't realize Colormount wasn't archival though. Now I'm confused. I think I'll ask John Sexton what he uses. I can't remember for sure.