Part Number : BMR90054. Original Design and Develop.CNC Aluminum.Anodized Finish.Stainless Hardwares.High Quality Materials.Quick Install w/o any modifications.Made in Taiwan.
www.dkdesign-global.com
There's also a slew of them on eBay, and most folks here have had good luck with Eoswing brand (from eBay.
I have one similar to the link posted above (different brand) that does in fact blank off the LHS large hole.
If you look at the top row of pictures from that link (although they show a cast wheel), that is the LHS blanked off.
The two hole covers coming in from either side are joined and tightened through the centre by a threaded rod.
Looks like a nice project for someone to do on a lathe.
Could use the same fastening technique as those above utilising a threaded rod through the centre.
Might create a market for "hub caps"!