Any trick to making a bunch of fake loaves of bread? I need to stock a bakery.

Fully line a metal bread pan with waxed paper (NOT
tinfoil or Saran Wrap) and then shoot into it some
expanding foam window insulation (available at
Home Depot's everywhere). After a couple hours,
the foam will bubble over the top of the pan, creating
that "freshly rised" look.   
When dry (read can for drying times) remove from
pan and peel off paper.
Of course, the thing will be bright yellow and not fool
anybody, so artful applications of paint will do the
trick. Or a light once-over with some brown spray
paint will carry the day from a distance. A coating or
two of sealer afterwards is also a good idea.
You can also make muffins, cup-cakes and other
assorted treats using this method with the proper
tins, forms or pans. (However, I imagine a bundt
cake would be horrendously difficult.)
Each one does take some time to dry properly, so
using more than one bread pan is probably a good
idea. You should be able to make a couple dozen
muffins from a single can of spray-foam. You may
get 2 or 3 entire loafs from one can.
Be sure to wear gloves, goggles and use proper
protection as this insulation stuff is wickedly sticky
and makes a fine mess.   Also, the pans should
NOT be used for baking or preparing actual food
afterwards. Keep them in your shop for storing
small items.
Cheers!

Shucks, ma'am, 'tweren't nuthin!

Another thing I neglected to mention: to save on
foam, cut a 2"x 4" block to size and place it in the
center of the pan. Staple some wire mesh (window
screening works OK) around the block to give the
foam something to adhere.

Not only does this save foam, but the wooden block
adds weight to the loaves so they don't bounce
around. Also, once finished they can be screwed
directly to your countertop, shelf, or bread wagon for
added security when the scenery is moved. (Muffins
are light enough to be merely hot-glued)

True, this process takes longer and is more
expensive than using treated, real loaves, but the
props will last longer and can be used for several
shows. Amortize their cost over many productions.

And since there is no actual foodstuff involved, these
loaves can be stored indefinitely anywhere.
Shellacked bread tends to get stale and will break or
crumble if handled incorrectly or dropped, resulting
in a multitude of crumbs. This might attract ants,
mice, rats or other vermin to your backstage. Or, if
you're in summer stock, then squirrels, raccoons
and bears (Oh my!)