Gents;
Best of my knowledge (and with some research...), there was NO 5cm Czech AT gun...
I THINK that HobbyBoss has kitted what could have been a prototype conversion using the 5cm PaK 38 gun... the barrel, recuperator, and muzzle-brake shown in that box-art all conform to the PaK 38 gun. Not knowing what's inside the fighting compartment ref the gun, I cannot say for sure, but... IF this is the case, HB has mislabeled their new kit by suggesting that this one has a "5cm PaK (t)".
The German 5cm PaK 38 was decidedly better in performance than the Czech weapon - but the Czech weapon was useful and available while demand for the 5cm PaK 38 was huge elsewhere, so in went that Czech thing into this limited-run conversion vehicle (and into some 202 "panzerjaeger Ib" built in 1940 - 41).
The Czech 4.7cm AT gun was not continued in production much past early 1940 - which probably attests to it being OK and quite useful but not sufficiently great so as to merit continued production under German direction, unlike the Pz 38(t) and variants).

I have no specific documentation of this 5cm version existing - but it seems that it may well have happened, given as the Germans tried out any number of possible mounts for their AT guns. The PaK 38 was rather larger and heavier than the Czech 4.7cm gun "normally" used in this conversion, and also had substantially higher recoil... maybe too much for this light chassis (but then again, the 5cm PaK 38 was successfully used on that SdKfz 10 light halftrack, so...)?
Cheers!
Bob