Sure. I just looked for "rocket iii fork tube"
here is the first one i found within a few seconds of scrolling though the used items.
2005-2017 Triumph Rocket III Classic Roadster RIGHT FORK TUBE LEG FOR PARTS | eBay
Since im sitting down now ill run you though my parts fiding prosses.
google it / eBay it. If no results are found or its hard to know what to call the part, go to a manual parts diagram and find the part number and take that back to step 1. Now shop around for that part number
here is a link to parts diagram. I looked for "fork"
FRONT FORKS & YOKES ROCKET III & CLASSIC ONLY for Triumph ROCKET III CLASSIC & ROADSTER # TRIUMPH - Online Genuine Spare Parts Catalog
looks like part is #12 and has the part number T2045529 and is like $60 from triumph plus shipping. So lets look for that part # on eBay now and also google. After a few minutes of that looks like some places have it but its about the same cost. SO a used one for $45 with free shipping or local pickup in ohio seems to be the right deal unless someone here has one for sale they could get you for less $$. I bet you can part out that fork assembly, keep the nut and make back your $ easily from the lower guard and bracket. its funny someone also said pinwall for parts, i just noticed that this is from them!