If you can find someone to make the print (and 46x60" is an odd size, being just a little bigger than a common 44" printer can handle), I've had good luck getting art supply places to mount really large pieces. I had a show right before COVID that featured three prints in the 40x60" size range - all were within the capacity of a 44" printer, though. The same show also had a couple of panoramas that were printed on my 24" Canon Pro-2000, but were as much as 8 feet long.
A local Dick Blick Art Supplies (the one I used was in the Boston area - although I'm in San Francisco now - a quick search reveals four in the Bay Area plus one in Sacramento - of which Berkeley and one of the San Francisco stores have frame shops) was able to dry mount these pieces to Gatorboard at a very reasonable cost (well under $100 per piece). I did have to call around to several Blick locations to find one whose dry mount press was in an unobstructed enough spot (and whose framer was creative enough) to handle the large pieces. If neither of the Bay Area Blick's with frame shops can do it, I'm sure there are other places that can. Prices vary really widely, and I have found art supply stores (or camera stores) with framing departments to often be MUCH cheaper for this kind of work than the average stand-alone framer. With Blick's, watch out for the omnipresent sales - they send out multiple junk e-mails per week, and they often have a discount on framing (which includes mounting). At least when I last dealt with them (pre-COVID), anything less than a 40% discount wasn't worth using, and 50% was occasionally available.
The bigger challenge is going to be getting a really good 46" wide print made. The ideal machine for this purpose is a Canon Pro-6000 or Pro-6100. None of the 60" or larger Epsons use the full photo inkset (the P20000 is pretty close, and would be another good choice), while the 60" Canons do. The range of papers available above 44" is also quite a bit less than you'd find in 24" or 44". Only about half of the Canson Infinity papers and 1/3 of the Hahnemuhle and Moab lines are available in 60"width. Finding a place that caters to photographers and has one of the few real photo printers in a 60" width plus the paper you want may be a challenge. Bayphoto (as an example that has been mentioned here) doesn't do inkjet over 40" They do have a Lightjet or something similar that goes up to 50"...
Dickerman Prints in SF does do 60" inkjet (it looks like on some Epson or another) ,and they're a high-end place that works with photographers. They'll mount to a whole range of things as well (more money than Blick's, but they'll mount to some high-end materials that Blick's won't)
