If you bodge up your own fork, you can use a standard 100mm front hub.
If you’re going to buy a fork get the Salsa Enabler which uses a rear hub. The advantage of that is that you can then use a 100mm wide rim for maximum flotation. (It’s nearly impossible to get a 100mm rim and fat tyre through 100mm OLD dropouts).
But you can try the whole thing for the cost of a fat tyre and tube if you do it my way.
Of course if you really really want a huge front wheel, then you could try this
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My recumbent fixed wheel folding Penny Farthing – bodged up from assorted parts.
Edit: another advantage of bodging up your own fork is that you can tailor the front ride height so there is less effect on the geometry of your bike. A fat wheel is like sticking a 29er front on your bike – ok if it’s a 29er, but slackens your headangle quite a bit if it’s a 26″.