TLDR; Easiest passive thing to do is keep looking. Otherwise you may end up forced to DIY, though that could get expensive and/or time consuming for what it is.
Frankly I wouldn't do any of the below, instead I'd cut a hole size for the largest (especially deepest for longer life and better flow:noise ratio) traditional axial fan that will fit, an intake fan so you are pushing more, rather than less air through the PSU than if you added an exhaust blower. This could make a significant difference in a SFF PSU's lifespan. I'd shoot for a 92mm x 25mm if it'll fit.
A cut hole on painted metal can be ugly (or not so bad if you have the right size hole saw and paint the cut edge to match) but you could finish it off with a filter panel over it, or cheap ~$2 pack of black automotive door edge guard molding from a local auto parts store. Power, get an adapter off ebay, or get a molex 4 pin splitter assuming the system has at least one but it's in use? Adding a small fan will be a negligible difference in current for this purpose. Heh, I don't know your past PC moddin' experience so whether this type of thing needs to be mentioned.
Other DIY options...
Take a low profile bracket with the typical two tabs 'n screws, cut a piece of circuit board (or aluminum, steel might be too heavy) large enough to mount the fan on, drill several well placed holes in the bracket till it looks like swiss cheese, then pick the size fan you want on it from Digikey, and while at Digikey get an SATA plug, or get an adapter plug off ebay cheap ($1?), or saw one off an old dead HDD/etc and solder it up.
Option 2, I can't tell how tall that fan is, but you might be able to just cut down the bracket on it to be short enough, or not, depending on how wide the airflow exit hole is.
Option 3, make your own bracket out of steel or aluminum, though you might need to heat the aluminum to get a sharp enough bend at the top w/o cracking it, and you'd at least need a bench vise and hammer or better still a metal brake to make that bend.
You do realize that this type of fan is quite loud for the amount of air moved? Granted any addt'l airflow beats nothing, but connected straight from PSU SATA, removes the opportunity to adjust the fan speed.
Well not entirely, through experimentation you could add a series of diodes or few tens of ohms 2W resistor in series on the positive (or negative) power lead to slow it down but like all the above, this requires some DIY rather than plug 'n play. Another option would be get an SATA adapter dongle of ebay and swap wire positions to get 5V powering the fan, if you pick one compatible and still retaining enough airflow at 5V which is sort of hit or miss unless you had a variety of fans to test.
Getting a pack of diodes and soldering on one after another as you test the resultant noise and flow rate is the surest way to a solution with the noise:airflow ratio you need, with a single purchase of diodes, unless you happened to have a variety of 2W resistors in roughly 22 ohm to 120 ohm range to experiment with.
The cool kids might 3D print a low profile bracket. Another option might be swapping a faster fan into the PSU, though it might require soldering and will definitely increase noise. If you have a particular hot zone you might be able to cut a hole, slap a filter panel on adjacent to that zone and let the existing exhaust fans pull air in there.
I've already written too much, do you have any willingness to go the DIY route with any of the above?
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