(Like everything else in the engine bay, I painted the reservoir black
The rivet nuts, as well as the nutsert rivet tool, I got at Harbor Freight.
Here's my parts list from McMaster-Carr if you want to duplicate:
5350K34 - 2x - Zinc-plated steel Barbed Hose Fitting - 5/16" hose, 1/4" male NPT
5269K313 - Metric Steel Compression Tube fitting - 10mm tube, 1/4" male NPT
4464K212 - Stainless Steel 1/4" NPT coupler
The Derale cooler I got came with hose and had the 11/32" hose barbs ends.