If you do need to look at trailer parts and see what you might need then I can recommend AUTOW (
www.autow.co.uk) who have an internet shop for just about everything to do with trailers you could ever want and a good variety to fit different makes.
If you look through their spares pages on their web site they give dimensions of bolt holes for suspension units so you can buy to match what hole arrangement you have in most cases. Units come without hubs which you buy separately from them to suit your wheels.
They sell imperial and metric hubs and shafts with different wheel/hole arrangements - just needs a bit of research on their site once you have measured up your trailer.
They do complete 500x10 wheels and tyres for approx £30 complete if you want to uprate (probably advisable for 2 up on motorway).
I have had about 4 lots of bits from them over the last 6 months (building new patrol boat trailers and repairing others) and they have all been delivered within about 48 hours of internet order. I have not been able to better their prices on the internet or elsewhere.
One thing to note is that most of their hubs come with a grease nipple and this needs a 'cutout' in the wheel - where the hole for the hub is - so check your wheels before ordering hubs otherwise filing or angle grinding is required on the wheels.
regards
Steve Willis