You might try calling:
Baker Motorsport Co.
8124 West Fwy
Fort Worth, TX 76108
Call us at +1 (817) 834-1392
Ask for Tim.
At one time, Kevin, the guy who owns this site, imported all of the Royal Enfields from India into the USA.
They had all of the parts to totally rebuild all of the old RE's they imported.
Tim worked for them and knows the old Iron barrel like yours like he knows the back of his hand. He kept up with the changes RE made and is probably the most knowledgeable guy in the US about their parts, from the Iron Barrel thru the AVL Lean Burn to the new UCE's.
Times changed I think a lot of the parts they carried ended up at Baker. Tim ended up there too.
I'm not sure if they have the parts for your motorcycle but they might. Only Tim will know for sure.
If they don't have what you need, you can still get all the replacement parts you want or need from Hitchcocks in England.
They have it all. The only problem is if you live in the USA, it takes a while for their shipment to get here and, their prices are moderately high.
A lot of the stuff you will find on the web might also work. Most of it is from India and while some of it is fine, some if it is pretty shoddy.