Big Foot Problems

That's a big kid! Maybe get the 17's and have him wear an extra pair of socks?

A lot of hard to find stuff, like size 17 shoes, end up on eBay.  Retailers have a hard time selling these items, that they sometimes get via forced distribution from manufacturers, in a retail store with limited foot traffic.  They either dump these items on diverters who sell on eBay or sell them directly on outlets such as eBay that attract a huge audience.  For example, an eBay search for "size 17 baseball cleats" produced over 400 returns.  Maybe only 50 of those are relavent but where else are you going to find 50 pairs of size 17's to choose from?

It you do find the perfect sneaker, you can get http://www.customcleats.com to turn it into a cleat.  Not cheap, but you may not have any other stylish options.

Outlet stores.  We have Adidas and Nike outlet stores here in my town that will open back up on Friday.  I will try to run out there first of next week since I will be gone on Friday and Saturday.  They normally carry 17's and 18's.  Not many but they do carry them and they are normally cheap.  Check several of the baseball websites.  Eastbay has New Balance 17's.  Just checked a few.  When my son's foot grew, not like that, we were able to go wide for a year before we had to grow longwise.

I thought I had it bad trying to find 13.5s and XL socks for my kid...    This is not profound advice, but online shopping is my go-to.  I just checked out Zappos.com (owned by amazon), and they do show some athletic shoes, including a few styles of cleats, in sizes up to 18.  (No half sizes above 14.5 though.)

Maybe find a basketball version of HSBaseball web and post a question to find out what parents of kids who are 6'8"-6'11" do?

I think the problem w/ Big Foot is that it actually is blurry. 

I feel your pain.  One of my sons wears a 14.  He orders strictly online now.

Check online, eBay,  Zappos, etc. as others have mentioned, but remember stock may be down because China closed down production (Nike, UA, etc).