Maybe he'll get them from defeating his monster of the week.

Depends on where they wanna go with it. His Power Ups could simply be Souls based on other persons. Those he could just find at one point in the story since they are searching for the remaining Eyecons.

I wonder if Ghost's base under suit will change at all until his final form. Assuming his final isn't just another parka.

It should be noted, Ghost's Eyecons so far go up to number 7. Spectre's start at 11. This implies that Ghost will get another 3 Eyecons from the "great men" group at least. That would be enough to account for his early-series, mid-series, and final upgrade. But I think it would be kinda weird for some eyecons to randomly be more powerful than the initial ones. So....who knows.

Spectre will also probably (not definitely) get an upgrade at some point, so that's another thing. Either he gets Eyecon 13 or it's some other thing (and if it is some other thing, it's likely something Ghost will also have). We're almost definitely getting at least a third Rider, and it would make sense if they got at least 14 and 15...

Personally, I'd love it if Kamen Rider turns out to be exactly the same in Ghost's universe as it is in ours: a kids show created by acclaimed late manga artist Ishinomori Shotaro. That way, when Takeru dies and gets the Driver, he thinks to himself "Huh, I look like one of those Kamen Riders." thus taking that as a mantle. Then, when its Final Form time, Takeru aquires the ultimate Eyecon: the Ishinomori Tamashii.

That'd be pretty freakin' awesome. Would screw with continuity immensely though lol

Kamen Rider has a continuity?

I’d love that! :D

Yeah, but it means we'd get a Rider with a crazy fro.

It would be harder to do crossovers if they have a Kamen Rider show set in our world. Seeing that Toei has made the rider shows set in the same world as each other since W.