How hard to find marinas for boats > 60 feet? (US)

Of the marinas I'm most familiar 50' puts you in a different situation. Probably 90%+ of the slips in most marinas are for boats under 50'. Once you cross 60' you're into more select, upscale marinas or commercial shipyards.

And Nycap is talking NE while OP wants west coast. So let me try West Coast. It's a huge long area with many different characteristics.

First, transient dockage is not a problem along any of the coast for your size. Permanent dockage is then what I'll discuss.

In San Diego, it's readily available as long as you're not bothered by price. In Los Angeles, length isn't the issue, just availability of slips is and waiting lists are common. In the San Francisco area, length can be a limiting issue as many marinas are geared toward smaller boats, but there is still dockage fairly readily available for your size.

Then there is the Pacific Northwest. Specifically, in the Seattle area, dockage is very tight and waiting lists may be long. The further from Seattle the more readily available. One issue in the area is that there are a lot of mooring balls, but none for boats this size, so they remove some boats from docking but free up no slips in your size. Still as you move away from Seattle slips are more easily found.

Now this is without even talking Alaska.

I don't know if you've always lived in Europe or recently, but one thing one loses sight of in Europe is the size of the US. San Diego to Seattle is over 1200 nm, about the distance from the south of Portugal to the Netherlands.

In general, the size boat you're talking about is not a very limiting factor on the west coast, but you may find slips to be limited, especially in LA and the PNW.

One thing Nycap alludes to is that many of the smaller, cheaper marinas may not be able to accommodate you but larger, more expensive ones may.