B&H has them in solid and gels from 2x2" up to "real big". 

Scott, get a sheet filter in ND (4x4" or 6x6") and hold it in front of the lens with a stiff wire and alligator clips. 
Or, you can just hold it by one corner with your fingers if you have a free hand.

You might try a different developer, Scott.  If I remember right, Microdol-X and Perceptol usually produce slightly less than
full film speed.  Some small decrease in dev time along with the other normal characteristic of those two developers
may work well for a pull.  I'd try it out on 35mm or MF to be sure you get what you want.  10x12 is a little dear for experimenting.  
Or, use an ND filter and shoot like normal but without the filter factor?

It looks quite soft, Scott.  I mean the lens, not your work!  Makes me wonder how you
pick a place to focus with that one, and how it looks to you on the glass when you're doing it.
I think I would definitely need to put a loupe on the glass to find the "sweet spot" with
that one. 

Haven't seen Maddie and her momma in quite a while, Scott.  Nice to see them in your photos again.
And, the big boy too, of course!

Been a long time since I got that many good shots in one session.  All very good, Will!

That's pretty neat, Scott.  Sharp eyes, and the gradual transition to funky duty.

I enjoyed all of these, Bill.  Especially "Walking Wall St.".

Beautiful, Scott!  I like daffs, and I really like that shot.

Nice shots, Dan.  The one of Katie is quite precious.
I think the sepia looks very good on Anne.  It warms her skin and puts some "gold" into her hair.  Looks good.

Oh, it looks nice, Scott.  I'm one of those who really likes the Canon RF magnifying thingie.
Very good for my eyes, and just an all around nice camera, too.

Thanks Craig!
Again, and again, and again, Thanks!
I checked four or five times a day to see if the ogre stompin' was still going on.
Today, all fresh and new.  The world once again spins on its axis.   

Now, twice in my current session, AVG has blocked what it calls "threats", once as I logged on, and
once as I opened the "F Stops Here" part for the forum.  Both times, it (AVG) asked which option I
would like to deal with this Blackhole Exploit thing.  On my first opening of the forum main page, I was
able to remove two threats.  On opening into this part of the forum, (where I'm typing this), AVG asked
if I wanted to read more about it or send it to the "Virus Vault", which is what was done.

I didn't get the file numbers on the first two pop up windows.  I can try to do that if there is a next time,
if it will help chasing this down, Craig.

Dean

I'm getting a similar warning from AVG on the "Blackhole Exploit Kit" for Nelsonfoto.  Yesterday it blocked the
forum completely.  Today, it's letting me in, but keeps flashing a "Danger, Will Robinson" warning box.

Ya got me with that third blowup.  That's some sharp looking stuff!