In the US Hooker Harness will re-web your current belts.
Assuming the metal bits are all in good shape it is significantly cheaper to re-web than to replace the entire system. Most (all)seatbelts have a 12 year life limit due to UV degradation of the material. The tensile strength goes down drastically due to this degradation. For about $150 it is certainly worth sending them for re-webbing during the off-season.
If you are in Canada, use GJ's Aircraft belts. He does a super job.
www.gjsair.ca
Dave Springford
www.foxonecorp.com