I think a lot of us use what is known as a "cows knee". I've made several as gifts and mine tie onto your triggerguard with a couple of leather thongs. The cows knee then comes up and over the primed flintlock and is secured with another leather thong that I wrap a couple times around a bone or pewter button. There also known as lock covers. The Leatherman sells a commercially made one for $15.00. Just google The Leatherman and you'll find one under leather accessories on their site.
This is what I use; it's made with Chamois leather used for car washing and saturated with Sno-seal. Slather the Sno-seal on and then dip it in hot water and work it in real good. Let it dry and recoat with Sno-seal. It should be waterproof then. Test it by drapping it over a drinking glass and put some water on top; if it goes through in a couple hours then retreat with Sno-seal. Once it's waterproof take off the excess so it's not so sticky with a shoe shine brush. The older the cover gets the better it gets. One of mine is over ten years old and will pass the water test for weeks and never go thru.
It molds itself to the gun and lock and will stay put; it's an outstanding lock cover. You can make several for about 12 bucks. You just have to make and use one to see for yourself; posted many times but never hear back on how they like em. I have used the commercial ones and like these a whole bunch better. Try it and you will like it.
Ill chime in a great idea just in case you dont get one or make one in time for this year----LOGGY uses an empty bread loaf bag with both ends cut open and then slid down the gun over the lock ---- add one rubber band to one end and another to the opposite---cheap and works!!!
I got my Sno-seal at Agway and don't know for sure if Mink oil would be totally waterproof; but if you don't have Sno-seal I would try it to see. Mink oil probably wouldn't stick to the gun the way the beeswax Sno-seal would.