There are a couple of sources here in the states. I own an '87 X-1/9 and I assist with the Western New York chapter of Fiat Lancia Unlimited (a club of about 500 members and their Fiats, Lancias, and Italian others across the US).
www.flu.org is their website,
you could check out mirafiori.com, or look at C. Obert and Co (Fiat Plus) in california... I know they have a nice dallara kit that you can put on your street car if you dont mind dropping $3500 US. The folks at C Obert should be able to point you in the right direction.