I found the rear brakes on ebay.de, they were also on the autoparts24.eu. Theoretically, on the site was cheaper, however, when counting shipping to Poland they were much more expensive. Each form of shipping to Poland was very expensive and on average profitable, but thankfully with the help of iichel, who ordered the brakes to the German address, and then sent them to Poland (in this way, shipping was much cheaper). As it turned out later, the rear brakes from Polo WRC Street came all the way from Sweden.

Here is my full list of part numbers needed for the brake swap to those from the VW Polo 6R WRC Street 2.0 TSI.

Part numbers to rear brakes:

6R0615423B — Brake caliper housing, left
6R0615424B — Brake caliper housing, right

6R0615425D — brake carrier with pad retaining pin, left
6R0615426D — brake carrier with pad retaining pin, right

6R0615601A — brake disc 254×22 (I bought Zimmermann Standard Coatz 600.3244.20)
6R0698451 — 1 set of brake pads for disk brake (I bought Ate Ceramic 13.0470-2820.2)

6R0615611A — cover plate for brake disc, left
6R0615612A — cover plate for brake disc, right

6R0609721K — brake cable 1659
6Q0609639B — bracket for brake cable, left
6Q0609640B — bracket for brake cable, right

N90740302 — socket head bolt with hexagon socket head (combination) — 4 pc.
N90937002 — hex socket head locating bolt, D >> — 14.12.2014 M6X16 — 2 pc

6R0611763F — brake pipe/hose from brake hose to brake caliper housing left rear
6R0611764F — brake pipe/hose from brake hose to brake caliper housing right rear

Bolts

N90937002 – hex socket head locating bolt, D >> – 14.12.2014 M6X16 – 2 pieces (no. 10)

N90740302 – socket head bolt with hexagon socket head (combination) – 4 pieces (no. 14)

1J0501249C – cap – 2 pieces (no. 24)

6R0611763F – brake pipe/hose from brake hose to brake caliper housing left rear PR-1KT,1KK,, 1KV,2EJ,1KP,, 1K (no. 8)

6R0611764F – brake pipe/hose from brake hose to brake caliper housing right rear PR-1KT,1KK,, 1KV,2EJ,1KP,, 1KD (no. 8)

Brake caliper housings & brake carriers with pad retaiining pin

Left rear brake

6R0615423B — Brake caliper housing, left
6R0615425D — brake carrier with pad retaining pin, left

Right rear brake

6R0615424B — Brake caliper housing, right
6R0615426D — brake carrier with pad retaining pin, right

both brakes on autoparts24 (with shipping to Poland)

Brake cable

6R0609721K — brake cable 1659

Cover plates for brake discs

  • 6R0615611A (cover plate for brake disc, left)
  • 6R0615612A (cover plate for brake disc, right)

Hoses from brake hose to brake caliper housing

  • 6C0614749 (brake pipe/hose from brake hose to brake caliper housing left rear)
  • 6C0614750 (brake pipe/hose from brake hose to brake caliper housing right rear)

Brackets for brake cable

  • 6Q0609639B (bracket for brake cable, left)
  • 6Q0609640B (bracket for brake cable, right)

6Q0609639B (bracket for brake cable, left)

6Q0609640B (bracket for brake cable, right)

Brake discs