Wanting to use a scout scope on my 458 socom. I tried a Midwest Industries handguard and it walks off the barrel nut. Has anyone had success with a scout scope on a 458, and if so what handguard??

You need something like this...

https://www.breachbangclear.com/ultralight-monolithic-ar-15-upper-receiver/

You must have had the old Gen 1 or Gen 2 units. The Gen 3, and especially the Combat Rail, SLH, and Ultgra Light weight rails are not going to walk off the handguard and they not require the use of adhesive like the old Gen 2 rails did.  
That being said, IMO it is a bad idea to mount any optic on the handguard.  Too much flex even in the best of them. As said, unless you have a heavy-assed monolithic handguard, there is going to be some flex.  Mounting sights on the handguard are good enough for front sights that are designed for use up close and personal, but for a scope, I wouldn't recommend it.
You might be able to use something like the super extended ARMS mount that mounts to the upper receiver but extends way out over the handguard.  I had one and it worked very well, as well as being quite rigid.  link

Another option would be a GG&G scout rail.

This actually looks like the best option. It says AR 10 but unless I'm missing something AR 15 rail is the same

I looked at that but it doesn't seem to extend far enough

Never used any of them,  but depending on far forward you're trying to push the optic the SWAN or PRI that spans the gap of the receiver and rail might be something to look at. Tieing the upper to the rail with another section would provide strength,  stability and rigidity.

I still haven't figured out what sighting I will use on mine. Given the shorter range of the 458 that will be the limiting factor for a decision.