Pretty much any Ops-Core compatible cover will work with a little ingenuity. And by "ingenuity," I mean an X-acto knife and some tape.
Most covers that are "not" compatible with the Bump are considered non-compatible because the cover is intended to be "sandwiched" between the NVG shroud and the helmet, which you cannot do with the Bump because of the molded-in shroud. However, with almost any one of these covers, you can simply open a hole for the NVG mounting interface, and install the cover normally without any problems.
This is an Ops-Core cover I did a while back, before I made some... changes... to that helmet:
What the back side looked like after being stitched:
Of course, you could always be more drastic, and grind the molded in shroud off the Bump so that you can use a normal 3-hole shroud.
The Crye Airframe cover actually fits the Ops-Core profile pretty well, if you don't mind the gap where the Airframe's "vent" is, and comes in a version with a cut out already in the cover, which I based my Ops-Core mod on. This is a ballistic FAST, but demonstrates the basic fit of the Airframe cover to the FAST XP, which is the same profile (just go a size down for covers) as the Bump:
The Airframe cover is also fairly cheap compared to some Ops-Core covers.
Oh.
And P.S. -
Many companies make covers for the Ops-Core that already have cut outs for the NVG shroud that will work without crazy modifications or re-purposing with the Bump.
Both the First Spear and ODG both have cut outs that will allow them to be used with the Bump.
Just be sure to go one helmet size down when selecting a cover for the Bump, as most covers are sized for the much thicker ballistic shell.
~Augee