You can purchase online Slotted Spring Tension Pin (Roll Pin) Kits.
Available in both metric and imperial.
The following sizes are included in our Metric Spring Tension Pin Kit:
1.5mm x 8mm, 2mm x 5mm, 2mm x 10mm, 2mm x 20mm, 2.5mm x 10mm, 2.5mm x 18mm, 3mm x 12mm, 3mm x 20mm, 3mm x 30mm, 3mm x 40mm, 4mm x 20mm, 4mm x 32mm, 5mm x 14mm, 5mm x 26mm, 5mm x 30mm, 6mm x 16mm, 6mm x 20mm, 6mm x 2mm, 6mm x 26mm
https://springfasteners.co.uk/product/internal-circlip-kit-metric-qty-1-box/

The following sizes are included in our Imperial Spring Tension Pin Kit:
1/16″ x 1/2″, 1/16″ x 1″, 1/16″ x 1.1/2″, 3/32″ x 1/4″, 3/32″ x 1/2″, 3/32″ x 1″, 1/8″ x 3/4″, 1/8″ x 7/8″, 1/8″ x 1.1/4″, 5/32″ x 3/4″, 5/32″ x 1.1/8″, 3/16″ x 7/16″, 3/16″ x 1″, 3/16″ x 1.1/2″, 7/32″ x 1/2″, 1/4″ x 1/2″, 1/4″ x 5/8″, 1/4″ x 1.1/8″.
https://springfasteners.co.uk/product/spring-tension-pin-imperial-kit-qty-1-box/