Lapras whereabouts

best and likely only bet is to hatch one from a 10k egg...odds of finding a wild one are slim to none.

Eggs
I've even tried praying but no popular deity has replied yet

Either hatching from 10k eggs or looking for water biomes, that's where I've found my first one, but they spawn rarer than dratinis.

I have only ever seen like 2-3 in the wild and most if not all of them were during special events like the March 2017 water event. Most of mine have been hatched, if you find help you can get them in boss raids (when they are in the cycle), but it takes like 4-5 players I think to beat them.

Buya lot of incubators.
That way you'll find way more 10km eggs, and increase chances of hatching a Lapras.

In addition to the things already mentioned, you can also hope it comes back as a raid boss and you'd be able to obtain it that way.

To save money from buying tons of incubators, it’s about one Lapras out of 50 hatches from my experience. Maybe you try to wait till Lapras raid boss in December.

Tier 4 raids, it will come back.

Hatch. They are rare in the wild, and even then (barring an event, research quest, or community day), the chances of getting one with good IVs is slim.

Unfortunately, the time to hatch a good one was early on in the game when the 10K egg pool was smaller.