Certain specific scallop shell designs will obviously be proprietary, such as the ones used in various regions or by various local pilgrim associations for official waymarking purposes, which will be more protected than other deigns so as to avoid their misappropriation and misuse by third parties to the detriment of hikers/walkers/pilgrims wanting to follow those waymarks in a reliable manner.
Many other designs might be proprietary, but potentially free for re-use, or with easily obtainable permissions, etc., but basically these are brands
I have no idea how one would go about seeking information regarding any single specific existing design -- and I feel that it would most certainly safer and easier to just create one of your own, perhaps similar in look and inspiration to one that you like, but nevertheless still unique and different and your own to do with as you please.