One idea I have...The post-2000 Campagnolo 9/10 speed rear derailleurs are interchangeable, so I can use that. I currently use 9s shifters with a 9s Chorus short cage, and I bought a used 10s Chorus with medium cage. I guess I can swap them and use them on 9 and 10 speed, if I upgrade the shifter internals. LBS insists I should use a 10s chain with a 9s anyway, so I guess this is the best bargain I can do for now? I have quite a cadence, so I can use the 9s 14-28 with the medium cage 10s. I do not like the 13-28, as it lacks a 16T cog. A 14-28 will be close to the 10 speed 13-29, without upgrading the shifters...
My other option is to order some 11s levers, chain and cassette, and make LBS try if they work fine with my 10s FD and chainset. If not, I can return the levers and cassette...