I didn't see any google results for conversation compatibility, so I suspect that you could just make your own - it doesn't have to be perfect at all. Possible categories of conversations you could encourage could be things like books, music, food, relation to the new bride and groom (congrats mosb), human psychology, or travel.
Thanks Manfred!
Does anyone know of a freely available, short personality test that would be appropriate for estimating pairwise compatibility for wedding seating?