Tried a few Turners, either they never had the forms or they did but now the DOJ has them online.

Checked the DOJ site, and can't find the form.

Is it the same form as the Assault Weapons registration form, the heavy weight paper, off-white in color, rounded corners on top, stick thumbprint in upper left corner form?

Or does anyone have a DOJ link?

call the doj leave your name and address and they will mail you one

I agree with what Bill2k said and I don't know where in CA you are, but I picked up two of the forms from the Turner's in Norwalk.  It is the same kind of heavy weight off white cardboard/paper.  BTW, if you can, do the prints yourself.  I had mine done at the local PD and they treated me like they were booking me.    Stand behind the line!      Right hand, thumb out!     Step back!     I was waiting for them to tell me to strip down to my boxers.  This is after eying me suspiciously for the ten minutes it took them to pass it around and read it.  To make matters even worse, after printing me the guy made a copy of the form without my permission and filed it away somewhere!  Oh well, it's not like they can't get that info anyway I guess.

Note to self: Get finger print before filling out!

If you pick up your registration card at a gun dealer (i.e., I picked up mine when I went in to DROS my group-buy lowers), then they should have an ink pad for the DROS thumbprint, anyway. Just give it the thumb while you're there. No glaring cops, no involuntary strip searches (if you opt for a voluntary strip search, please don't tell us about that), and if you're there buying off-list lowers, then you'll be getting your thumb dirty anyway.

There's some stuff like FFL or COE applications that require the whole fingerprinting routine at the local PD, but the .50BMG app just needs an un-witnessed do-it-yourself thumbprint.

Back when I was a kid, we had ink pads for our rubber stamps. Nowadays, I guess kids just use stickers. Kids these days have it easy!

I called DOJ and requested the 50BMG form. It showed up in my mail box 2 days later.

Ha, I went in uniform down to one of the local p.d.'s and one of the hotties did my prints. No charge, no problems. Now that was for the military assault weapons permit.  
Had a smile on my face.  Maybe it helps that I regularly do police record checks there.  

Quoted: I agree with what Bill2k said and I don't know where in CA you are, but I picked up two of the forms from the Turner's in Norwalk.  It is the same kind of heavy weight off white cardboard/paper.  BTW, if you can, do the prints yourself.  I had mine done at the local PD and they treated me like they were booking me.    Stand behind the line!      Right hand, thumb out!     Step back!     I was waiting for them to tell me to strip down to my boxers.  This is after eying me suspiciously for the ten minutes it took them to pass it around and read it.  To make matters even worse, after printing me the guy made a copy of the form without my permission and filed it away somewhere!  Oh well, it's not like they can't get that info anyway I guess.

The form I have is the "Assault Weapon Registration Application" FD 023
*Index tap on top right
*Thumb print spot on Lower left side

Should be the same form, it's just the DOJ specifically states

.50 BMG Rifle Registration Application