Well, even the C64 had two CIAs, (older) 6526 (same with C128). 8520s even work in C64s, they're just faster and have additional timer(s).
The 1541's 6522s were just called VIAs (simpler, but very similar still).
Are 8520s hard to get? Vesalia has them in stock for 6.90€ (DIL) or 3.90 (PLCC) - no way to beat that price with an FPGA!
