In my P150 for example, the front fans are mounted to a hinged door which opens to reveal access to the inner drive trays which can be removed from the front.
The R4 could potentially do that, by either:
A. not using the front fans
B. tin snips and cut the handles off the HD trays.
The front fans are on a fold-down rack you can access from the front, nothing between them and the HDDs.
I don't know of any specifically that would work, but just doing a quick google, first result
. That would work just from top-down... and still make use of the bottom fan (blowing air up through the HDDs)... obviously SLI/Crossfire isn't happening.
It's a bit hard to tell but those 4 knobs on the top of it (look like rubber stoppers) might fit 120mm/140mm... if not... drill.
I'm sure there are ones specially designed for 120/140.... obviously anything that's basically a square box would work with a drill, and maybe some paint... I have lots of old PC's with 3x HDD cages... pop some rivvets, drill a couple holes... done.