Can anyone suggest a set of levers/changers for straight bars that would be compatible with a 9 speed Veloce triple setup?
Assuming it's post 2001 9-speed (so the newer shift ratios that Brucey alludes to), Campag did produce 9-speed Flat Bar Ergos. I've only checked the 2006 catalogue, but that lists Mirage ones - you might find a NOS set if you're lucky - but if you can find 10-speed ones instead, a switch to them should, I think, only involve the new shifters and another cassette. (A cursory google suggests they're not in stock in many places, though
Hibike in Germany claims to have a pair on the shelf.)
I'm not familiar with Campag bar-end shifters, but looking at a couple of the exploded diagrams, it looks like they come apart enough that you might be able to use them with bar mounts like Paul's Thumbies.
My Mavic rear wheel has a Campagnolo 8spd cassette on the hub but I am sure that the hub will take a 10spd cassette with ease by leaving the space out that is against the spokes.
If that proves not to be the case then I will limit the 10spd derailleur movement accordingly so as to be compatible with the indexing on the lever.
The splines are completely different between Campag 8 and 10 speed freehubs. You will only get a 10 speed cassette on an 8 speed hub with either a miracle or surgery.
The sprocket spacing is different between Campag 8 and 10 speed cassettes. If you try to use 8 speed levers and a 10 speed cassette, the indexing will be grossly inaccurate. If you try to use 10 speed levers and an 8 speed cassette, the indexing will also be grossly inaccurate. That leaves aside the difference in cable pull ratios between 8 speed mechs and 10 speed levers (or vice versa).