I purchase stuff overseas all the time and "Knock on Wood", I've never had a problem. Most of these businesses cater to US customers since we were the largest end user of many foreign made machines. If you have a credit card like Visa or Mastercard you shouldn't have a problem. If they take PayPal for E-Pay and you have an account, this is likely an even safer way of dealing with overseas purchases.
This outfit has the British Association and British Standard tools you will need plus fasteners and tap & die tools too and their prices aren't too bad considering how much tools cost now days. I bought all of the wrenches and sockets from Snap On back when they still made them. I'd hate to buy them now. The prices would break the bank. www.britishfasteners.com/
The outfit I bought all my tap & die stuff from catered to the aircraft industry back in the day when Rolls Royce engines were still using the old system before they went to Unified Standard. They are long out of business now. I'm pretty sure you can even get Heli-Coil stuff for the BA and BS threads but the kits are pricy.
A fellow in Australia had some headlight brackets made for the big General Electric headlight that the Chief used.
www.re-indian.com/ I don't know if anyone repros them or not. they are similar to the Guide types used on the early to mid 50s Harleys. The instrument panels for the Chiefs show up on the Bay now and then but they will cost you. The panel is where the amp meter, headlight switch, and speedometer were all housed. You might have more fun with this project if you just find the bear essentials for now and scrape the original type stuff up later. It's way better to get it running first then fix up on it as you can afford the time and expense. Lucas electric stuff was made so long that there are a lot of aftermarket parts that you can replace old stuff with like the old alternator and the recifier set up. You can wire it with the newer stuff and get your electrics going. Find a decent aftermarket custom or Bates type headlamp. You can switch it to a Boyer electronic ignition but if the old coils still work you could get it running with a few new ignition components from Hitchcocks. My guess is that whatever condenser it has was crap when it was new so you'll definitely need a new one of those plus whatever else is worn out. That thing really just needs a lot of cleaning, some new paint here and there, and a complete going over & relubrication of the chassis and drive system components. Someone went to a lot of trouble to lace those wheels with the aluminum rims. You can probably find some gaiters to fit or some tubing to cover the front fork uppers with. They originally had short tube covers on there. Keep it simple and have fun with it or it will set too long.
Kerby