running boards

I would look under your rig and see how your running boards are attached. That may help determining what can be attached. After that, do a search for running boards for your chassis and/or contact some shops that do that type of work and see if they can help.

I've seen E450 bus conversions with running boards that are a foot wide.
Now where you can get them will take some research.

We have a 2019 Ford E450 chassis on our Jayco Class C. The running boards are stardard aluminum, wide enough to put half (or more) of your foot on to climb in/out. I would assume they are same as yours. Doing an internet search shows me they are pretty much identical (some were colored all black, some where just the aluminum natural color). I doubt they are specific to Winnebago, as it bolts/attaches to the Ford chassis/cab.

Point is, you could check online with autoanything website (just one of many) or go to a local truck accessories shop (where I live near Peoria, IL there are 2) that does running boards, window tint etc. They can look up on an E450 chassis and see what is available. I know you said you don't want to replace but worth checking.

Lastly, a suggestion might be a local fab shop. If they are good with aluminum, have them weld/bolt panels to widen them as you wish. The RV portion of the CLass C is like 8 foot wide, but the cab is not...so you have room to play with.