At a glance, I think the more difficult part would be making the platform underneath the little twin-turrets. For the actual turrets if you were willing to go with fewer or more barrels you could find a heap of options:
Kromlech, for example has a number of Rapier-sized turrets:
https://bitsofwar.com/24-weapons?p=2
(Middle of the page, notably the Quad Mortar and the Storm Cannon)
They're approximately this kind of size:
Skip the tracked carrier - the turret piece is separate and sold separately as seen above.
Again though the issue would be building the structure to hold these two turrets in place? But, maybe something like that?