In the Uk, all places that sell Honda parts are tied in to Hondas price list. All suppliers quote the same prices, give or take a few pence.
Dealers also quote the same price, but often, since they are getting deliveries every day from their suppliers, they don't charge postage and packing.
Fowlers is one of the biggest suppliers in the Uk, very fast, but you have to pay postage.
David Silver Spares list items that they consider to be good substitutes alongside their honda parts.
After that it is down to making your own from standard tube, gasket material, seals .... I wouldn't know where to start.