Hi Dave
Once you get a bunch of B licenses (looks like at least one B4, one B2 if we're talking 7.62x51/.308 and one B5 for the 22LR conversion - by the way you should always request more licences than what you plan because it usually takes months to get them) there comes the fun.
While the AR15 market is much better these days with a lot more stuff from the US, we still lack real custom shops (there's the French Hera Arms distributor who can build stuff to your specs and Hera has heavy barrels).
You might be better off focusing on the core stuff (barrel, handguard) and then put any extra stuff yourself (stock, grip, trigger, ...).
And you can also look beyond borders: Luxembourg, Germany, Belgium ... Customs paperwork is not a big deal (takes a week and a half on the French side).
Here a few distributors in France:
- http://www.ste-equip.fr/ : Oberland Arms, Stag Arms,
- http://armureriefmr.com/ : Guy's a bit of an asshole but has a decent range of stuff and sometimes has decent prices (for France)
- http://www.tlgunshop.com/ : IPSC oriented shop
But first and foremost you need to define what you want. "Competition use" can go from long range target shooting, to service rifle 200m to IPSC rifle or 3Gun. Which all have very different requirements (and rules to comply with).