Magpul forend is a good way to go , you'll have to modify the forend some with a hole saw to fit , easy to do , even a thread on here about it .
Cheapest way to go, is just mount a magpul rail section on your current forend .
And then there's the GG&G option, which can be had with a sling point, which will work with a magpul para clip.
ht tps://www.gggaz.com/mossberg-590-sling-and-flashlight-combo-mount.htmlt tps://www.gggaz.com/mossberg-590-flashlight-mount.html
Wolverine carry GG&G kit , if they don't have it on their website, call or email them , they will get it for you