karls59tr,
As RonR says, the longer wheel studs are available from TRF. There are two normal lengths for the Triumphs. A standard length for the steel disk wheels and a shortened stud for use with the adapter when used with the wire wheels. If you are looking for longer than standard length studs, good luck.
To find the studs on the TRF website takes a little more work then the Moss or VB website. But I like that TRF will have many parts that are not listed by the others.
To find the parts you will need the Triumph part number. Look the part up in the Spare Parts Catalog. RandallY has scanned the SPC as well as several other manuals and I would rather he provide a link directly.
With the part number go to the TRF website.
Do not use the search box in the upper right of the page.
On the home page look for the blue banner across the top of the page.
Inside this banner is a search tab.
Hover the mouse pointer over this tab and a drop down menu will appear.
One of the choices is Parts Database.
Now we can enter the part number in the left hand search box.
This may seem like a lot of work but I find it works great for me.
Results from the search will show up. If the part is used in a kit or has been updated with a newer number these will show up also.
The 4 different studs are:
114282 Stud Front Disk Wheels 3.98
114281 Stud Front Wire Wheels 3.98
100869 Stud Rear Disk Wheels 3.98
110365 Stud Rear Wire Wheels 3.98