This actually isn't all that difficult. Standard tubular deadbolts such
as Schlage have hardware on both sides plus the latch mechanism in the
middle.
There are two through-bolts that clamp the two sides together plus a
flat bar that extends from the lock cylinder through the latch mechanism
to the other side.
Longer bolts are the first step. These are usually a hardened material
with a somewhat unusual head to allow trim to cover the bolt heads.
The tailpiece is the tricky part, but still not all that difficult.
There are two styles.
If the deadbolt has a key on only one side, it's essentially a long flat
bar with a circular disk on one end. The disk has a cut-out section to
allow a little over 90 degrees of slop so that the thumb-turn can
operate without the rigid cylinder holding it in place.
If the deadbolt has keys on both sides, then there is a tailpiece in
each cylinder. These tailpieces are thinner but with a bump in the
middle. They overlap when passing through the latch mechanism. Same
principle in that either cylinder can operate the bolt without being
bound by the other.
The overall length of the parts will need to be customized based on the
actual thickness. Standard hardware will accommodate doors from about
1-3/8 to 1-3/4 inches thick. Any thinner and the bolts bottom out, any
thicker and they may not reach. So you will likely have to offer your
hardware in roughly 1/4 inch increments.
From a security standpoint there is often a metal sleeve provided for
the outer side that prevents someone from drilling a small hole and
inserting a "poker" to flip the latch hardware. If your gates are metal
this isn't a big concern. If wood you should consider offering
something along these lines.
Also there should be ball-bearings provided that are to be inserted into
the bolt holes on the outer cylinder to make drilling into and backing
out the bolts more difficult. These come with good deadbolts.
Buy a Schlage B-660 (single) and B-662 (double) deadbolt and this will
help you understand.
There are other makes and cheaper hardware but the Schlage B-660 series
is what I would recommend for this type of thing.