Gav, have you looked into IMAGE Wheels in the UK?. They don't show an FIA style but they do Halibrand in a 17inch so perhaps if they can get the outers they can mill up the centres.
Halibrand Replica Cast Alloy Wheels - Image Wheels CHB
Also, touch base with Bob at Vintage....vintagewheel@live.com as I know he has 17inch rim casings available.
Lastly, Dragway did me up some preliminary Billet sketches of some FIA 5 stud with spinner knockoffs as well. They may be able to offer the same in a 17inch?
Trigo's a no go as is team 111 I assume? Team 3 have quite a range in Halibrand 17's so perhaps they could modify to suit their FIA in the 15...
Dunno mate but enjoy the search. PS If buying from OS, make sure the supplier insures for ALL the wheels not just 1 or 2 as they did in my case. Twas a bloody nightmare getting it sorted and left me frustrated and out of pocket for quite some time.
How come 17's? Ive seen a few F5 Dattos in 17 halibrand but never FIA. Serpnts gone with 18inch Halibarnd, Ronnie Ford is 15 FIA and Im 18 FIA same as superformance but custom offsets. Not sure what SydneyChris did but I think Halibrand.
Also, are you looking to run lower profiles to the rear? I went the opposite and ran a much taller rear tire and side wall than the front. Did heaps of research on this and for a modern car version I wanted to get the Superformance look. Check out my topic in the Coupe Section of the site. Despite asking I didn't get much of a response.
tire (tyre) aspect ratio
Cheers Matt