I've restored 3 UO-18 mixtes, and just started my fourth this week, all with various styles of upright bars. The first I had the original Peugeot bars and plastic levers. The second I used the aforementioned Dia-Comp, the third, the Weimann. I got the Weinmann on Craigslist recently attached to some funky bars. All three styles look great on the bikes. The fourth I'm setting up for some serious riding in the hills of SF, with a triple crank, so I'm using a nice set of Forte levers that have a much more positive and secure feel. I've used the Forte with the Mafacs before and they work/feel great. Shimano makes a more expensive version. Neither have the vintage look though.

http://www.performancebike.com/webapp/wcs/stores/servlet/Product_10052_10551_1166937_-1___000000