The FB 21 is also the same basic machine as the Bolens G212 and Iseki TU2100 so you can also explore parts from that avenue. AGCO also lists new parts still available for it. You can look at parts diagrams etc. at AGCO Parts Books
One other alternative is to simply make your own. There have been several TBN members that have made heir own manifolds out of tubing and/or box section and they've turned out well.
The FB 21 is also the same basic machine as the Bolens G212 and Iseki TU2100 so you can also explore parts from that avenue. AGCO also lists new parts still available for it. You can look at parts diagrams etc. at AGCO Parts Books