I know it's a bit pricey, but American Autowire has a good reputation here. They also have a kit for A-Body Mopars. 1967-75 Mopar A Body Classic Update Kit | American Autowire
It's sort of a modernized reproduction replacement, so not sure if that will fit you needs. I know it definitely isn't setup for a Gen 3 Hemi, but at least it will get your wiring in check with modern fuses and better gauge wiring.
Other than American Autowire, there's also Ron Francis Wiring as well as Painless Performance for universal kits.
If you want to build your own relay box, and you just might so you can wire up the Hemi, then take a look at this series of instructions to wire up a Bussman Relay box.
Part 1: DIY Bussmann RTMR Fuse Block, Part 1 – Introduction | Bodenzord
Part 2: DIY Bussmann RTMR Fuse Block, Part 2 – Parts | Bodenzord
Part 3: DIY Bussmann RTMR Fuse Block, Part 3 – Tools and Techniques | Bodenzord
Part 4: DIY Bussmann RTMR Fuse Block, Part 4 – Wiring and Schematics | Bodenzord
Part 5: DIY Bussmann RTMR Fuse Block, Part 5 – Building the RTMR | Bodenzord
Part 6: DIY Bussmann RTMR Fuse Block, Part 6 – Installation | Bodenzord
Hope these links help.
