I had the same problem and tried to score some old seats here; but I got impatient and had new ones made.
I ended up going with Vintage Speedsters (black vinyl Spyder buckets with red piping) as they seemed to fit my budget best; they got them done in record time. I think Fibersteel makes a more "correct" replica seat, intended for original cars with a steel frame and proper brackets, but I have not seen one in person yet.
As far as installation goes- you will probably be drilling holes in your pan--odds are slim that your current holes are spaced properly. Try to get them absolutely parallel and use washers or spacers between the floor and the bracket to correct for the curve of the pan, IF you want them to actually slide back and forth. Otherwise just make sure the seat sits where you want it before you tighten the bolts all the way.
*edit* Whoops, you are driving a Vintage already; maybe you can reuse your current brackets? I would call and ask if the spacing is the same, that will save you a lot of headaches.
