My rolly-bags and large check-in bags are from Pelican / Stormcase, which have easily user-replaced, very nicely rolling heavy duty wheels. My large case (50 lbs+) just had a wheel fail after about twelve years, they sent me a new set, free.

Might be too industrial-looking for ya, though.

Have you called Heys? I've seen their wheels for sale on eBay (there's none there now, I just checked), but I'd always start by calling or emailing the manufacturer. ( [email protected] )
They might have things like that not listed for sale on their website, but who knows? They might just send some out like Pelican does!