I've used paperclay.co.uk for some time - it's just pre-milled and dried paper (cellulose) fibre, as used by potters, no additives.  Paperclay Products are the only source I've come across so far, although if you've got a paper mill in your area it would be worth contacting them to see if you can buy direct.  Comes in 2 qualities, standard is OK for most uses, fine (more expensive) for detailed modelling & smoother finishes.  I usually buy the biggest pack available (now 12Kg) as it's more economical, but I think they start at 2kg (fine) or 5kg.

Pros:  you control the type and proportion of pastes/glues and fillers according to what you want.  Saves huge amount of time, which was my main reason for switching from d-i-y pulp - I work full time so it's valuable to me to be able to mix up a batch of pulp and be ready to go within half an hour of getting home.

Cons:  it appears to be mostly recycled newspapers, so doesn't give the strongest mache.  If I'm building something large that needs to be fairly strong I'll use home-made pulp from photocopying/bank type paper (this is where the day job is useful - access to endless draft marketing proposals!) for the first few layers and then finish off with the paperclay fibre.  And you should probably wear a face mask when working with the dry fibres as they do tend to fly around a bit (doesn't matter once the paste is mixed in).

Cost -it's quite an initial outlay, but for me it's worth it when set against time, and all the energy used in boiling & blending.

:?
I don't actually find the making of pulp much of a problem.  Bringing a large (old) saucepan full of torn paper to the boil then blitzing it with a paint stirrer attachment in an electric drill works quite quickly.  For the rest, see Martin Favreau's article on pulp making.  Perhaps I resent paying for processed paper! :oops:
DavidO

Do you mean a kitchen mixer?  If so, they are GREAT!  The higher the power, the better.  My little old 175-watt was okay, but WallyWorld recently had a sale, $20 for 300 watts.  It's fantastic for pulp.

I know a lot of PM artists swear by paint mixers, but I'm not one of them.  They may be mixing much larger batchers than I am, however.  When I was mixing a small batch of pulp one time, I chucked the paint stirrer into my drill motor:  at full speed, I looked right down the shaft of the mixer and saw... nothing.  It was like the inside of a tornado:  empty.  A bit of the pulp was (barely) getting hit by the blades and slung off, but not much.  And the results after 3 or 4 minutes of using it were very disappointing.  Even a single old kitchen mixer blade chucked into the drill motor did lots better.  But, like I said, the size of the batch may have some effect on performance.

OTOH, paint mixers are designed for liquids, and paper pulp isn't a liquid even with lots of water in it.

If you have a cordless drill motor, get a couple of kitchen mixer blades at your local thrift shop (they usually have lots) and chuck one into the drill. 

Sue