Best way to add serial ports to STABLE machine?

[stan]

I've got a bunch of what I call "2nd generation" HP Vectras that I'm
redeploying for an application that gets input for Serial RS-232 devices. At
the moment the most input devices any 1 computer has to deal with is 2,
and I thought I would be in good shape using the on motherboard ports (as I
have done on the "first generation" Vectras). 

However, I just discovered that these machines have a 8250 serial chip
instead of a (useful) 16550A chip. Even ruining minicom against this port
locks the machine up :-(

Now, I can easily disable this port in the BIOS. 

So, whats the best (most FreeBSD compatible way) of adding an extra "good"
serial port or 2?

I've had success in the past with ISA card serial port cards to add 3rd and
4th ports. But I'm wondering if I can even still buy something this old?

Suggestions?

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
						-- Benjamin Franklin