Use the overrides to insert your RB only in those situations where and when you want him to play.

Dont look at overalls in FA, you could find quality back-ups under 60 if you look for speed. TEs and WRs are good options, personnaly i would go with WR.

Also, your own fullbacks are a good options to play while your HB is injured.

If you have to ignore the overalls, then your weights aren't right for RBs. If you're desperate, and trust me I've been desperate for RBs, then you only need to look at three attributes - Speed, Carry, and Avoid Fumble. Set those weights to something like SP 100, Carry 75 and Fumble 50 (some times I go 100 on all of those - my full set of weights are stranger), and then search for the best available player for those three attributes. Most likely the best FA is going to be an overlooked QB or WR that you can turn into a serviceable running back. Or an overlooked FB or TE that has a lot of speed, but no strength, that you can use as a big back until your players get healthy.

When I took over MFN-16, my top three running backs for the games that I managed my first year were:

1) some dude I found as a FA: https://mfn16.myfootballnow.com/player/3243
2) my starting TE (who is now back to starting TE): https://mfn16.myfootballnow.com/player/181
3) and a rookie WR that wasn't getting playing time (who is now back to WR but probably better at RB): https://mfn16.myfootballnow.com/player/4982

My current RB2 is also a former WR that wasn't getting playing time: https://mfn16.myfootballnow.com/player/3739

Those bozos managed to propel a 6-6 team when I took over to a championship. In short, it's not hard to find a RB if you're willing to play whoever fits.

i've done the same as setherick when i'm desparate for a RB only thing i would add to speed/carry/avoid fumble is to have as much acceleration as possible especially if you use outside runs a lot

edit: also, with high acceleration(85+) and low speed(40-50) i've had some success in the short game, i.e. 3-5 yards per carry, when the RB also has at least some break tackle (40ish) but you won't ever see a RB with those stats bust out a huge gain no matter how open a lane he gets since even if no one else gets him there's no way he'll get past the FS, he's just not fast enough

I don't put a lot of faith in AC. I've seen lots of top speed backs with low AC do fine.

Thanks for all your advice guys; I'll start a plan now!

I find acceleration to be of more use for WRs, or for slower FBs/power HBs, but I don't discount it as highly as you.