Ballscrews/linear drive

I know this isn't directly connected with the primary purpose of this
group, but I don't know where else to ask this:

I have been commissioned to build an automatic sliding door. It is a
very custom design, that is why the client isn't just buying a standard
off the shelf door.

I'm figuring using a Ballscrew would fit the requirements, with direct
drive from a servomotor. I can't use an Acme thread as I want to have
the option of being able to force the door open if power goes out.

I don't care if the ballscrew and nut are used and aren't accurate or if
they have lots of backlash. As long as they aren't so worn as to cause
problems like sticking.

I need two of them, this will be a two piece door. Does anyone here have
used ballscrews/nuts fitting this description, or know where I might
look for this? Trying to save a bit of cash without compromising the
integrity, obviously this isn't a need for high accuracy.

The other option I'm considering is something I found in the Small Parts
Inc. catalog. I can't locate my catalog to get the name of it, but it
sort of "climbs" a smooth rod as though it were a ballscrew. Anyone know
what I'm talking about?

Any help is appreciated. Especially names of suppliers in the
Tacoma/Seattle area, places that don't have a "3 question limit". :')

Thanks,
Steve Greenfield