Anybody know where I can find such at thing? Have a old, no longer produced treadmill & the transport wheels are shot. Not able to find replacements anywhere. Can find wider than 1" but that won't fit.

This is almost perfect, but this won't cut it for this heavy ass treadmill - Load approx. 125 -140 lbs.
https://www.robertbrooke.com/folding-bleacher-wheel-4-x-1-x-3-8.html

Caster Wheels - Mapp Caster

Maybe?

damn close but the bore isn't big enough

https://mappcaster.com/collections/wheels-all-4-diameter-wheels/products/4-x-1-hard-rubber-wheel-250-lbs-capacity

https://rebrand.ly/7e767e
2" wide, sorry
it's the bore size that defeats any finds, so consider a 3/8" bolt/axle if possible or sleeve adaptor

https://rebrand.ly/49001f
5" dia x 2.75" w, sorry

https://shop.servicecaster.com/4-inch-rubber-drive-wheel-p/scc-rss420-58-kw-2ss.htm?gQT=1
another near-miss

About to just settle on the ones I posted & take my chances with the weight.

Also shout out to Grainger. I thought I had found what I needed from Grainger.com
About 20 minutes after ordering I realized I'm an idiot & it had 5/16 bore instead of 5/8

Called to cancel the order and it had already been processed & loaded up. Impressive. Dammit.

4 Pack Steel Tri-Dolly, 200 lbs Load Capacity 3 Wheel Mover' s Dolly
might be a work-around if the object doesn't weigh more than 200x4=800# ... a fact still unknown

I wonder if you could drill out any of those hard rubber wheels to the correct axle size?

Ended up just buying the ones I originally posted. Turns out it wasn't actually a 5/8 bore but something communist slightly larger. Reamed them out and made the damn thing work.