think this depends on what rear uprights you've got, the earlier riots used a modified fiesta front upright and sierra callipers where the later cars used a sylva fabricated upright like this:
if you've got the fabricated uprights, they are designed for a vw caliper used on lots of golfs, passats, etc but this can give problems with clearance for handbrake cable and brake hose. the original recommended parts were these generic versions, https://www.compbrake.com/product/rear-caliper-with-built-in-handbrake-comp-r2/, but the handbrake cable is on the top and the hose fitting is on the front close to the driveshaft rubber boot. There are a few build blogs around for the sylva J15 which shares most parts with the riot describing this problem, such as: http://sylvabuild.blogspot.com/2013/05/revisit-rear-brake-banjo-clearance.html.
i used a golf mk4 rear caliper which puts the hose at the top and the handbrake cable at the bottom which seems to make fitting easier together with a caliper bracket from a passat. its a nice light aluminium caliper with handbrake mechanism but will not fit in 13" wheels and is tight in 14" (i had to remove a small amount of material from the ribs where the balance weights were close.
these look to be the same as i used:
https://www.ebay.co.uk/itm/203252869166?epid=249581092&hash=item2f52d0a82e:g:e8cAAOSwFJZgBvrS
https://www.ebay.co.uk/itm/223643956167?fits=Plat_Gen%3AMK+IV%7CModel%3AGolf&hash=item341237f3c7:g:OaAAAOSwJQxdaS~6
https://www.ebay.co.uk/itm/223643938039?fits=Plat_Gen%3AMK+IV&hash=item341237acf7:g:CWoAAOSwpZRdaSok
these are the brake discs to match (for the fabricated uprights), QH ref BDC3611:
https://www.autocraze.co.uk/brake-discs-matched-pair-2093.html
here's my final installation (on a J15 but fundamentally the same)
if you've got the earlier uprights i do have a pair of sierra callipers (i think) if you want them.
i've also got pdf copies of the original and later riot build manuals if you don't already have them
hope that helps