Many original TR8 parts are now NOS but there are various replacements available that will do the job just as well if not better from Amazon and the like. Below are the alternatives I have found as well, as other useful bits of kit to help keep your TR8 on the road. If you have any suggestions please do let me know then others can benefit.
Fire Extinguisher
Can’t recommend these highly enough, well worth having two around get them HERE https://amzn.to/3VPhLEZ
Battery Trickle charger
WINTER TIP For TR8’s that often stand for long periods of time given most don’t take them out in the winter very much and if you have more than one, you can’t drive them all at once. The solution I have been using for many years is a trickle charger that just keeps topping the batteries up as needed.
Get one from HERE 
https://amzn.to/4gFwbzy
You can connect a plug permanently to the terminals so you can quickly clip it on and off as needed. I have a battery that is 10 years old in one car and because I have always used this system its still going strong. Letting batteries fully discharge too often very quickly kills them. But if your do discharge the battery fully this gadget has various modes to breath new life back into the battery. Ask Santa or your nearest and dearest for one, you wont regret it.
Rubber Caps
Around the engine bay are various now unblanked tubes ends of screws etc when the rubber caps that once covered them are now all long gone. These rubber caps in various sizes do the job really nicely and are available HERE https://amzn.to/3UT6WR0
Works well for the rubber covers on the plenum catches, the originals for which were blue.
Note the use to neatly cover the tops of the SPAX suspension adjusters
In line FUEL FILTERS for carb TR8’s
The ones supplied from Rimmers have an olive adapter to fit the original carb system but the inlet is very small so these are a great alternative.
One on the Right is the original style with a much smaller hole
plus you can easily see the state of the fuel. Available HERE https://amzn.to/3WZG0lg
Clear see through which is a great improvement
You need to do a small mod by using a small piece of copper pipe fitted to the original carb olive connection as shown here. That then means you have rubber fuel pipe at either side of the filter and thus no need for an olive connection anymore.
Note the copper pipe going to the carb olive connection thus converting both ends to pipe
The pipe I used can be obtained HERE https://amzn.to/3x0bgpx
And the fuel pipe if you need it HERE https://amzn.to/3R0u3b2
And the correct curved fuel clips HERE https://amzn.to/4bA1cCU