Finding a timer won't be easy, but they are out there if you look hard enough. Find a copy of Kodak Pub. No. E-57 [no longer available from Kodak]. It should answer most of your technical questions.(posted 8517 days ago)There are lots of advantages, mainly the ability to sit back and let the timer do the work! No dip & dunk! The negs get great agitation and even development. You can easily find 3 1/2 gal. size stuff [made for 8x10 work] but that means lots of chemicals to be mixed and kept up. Since I wanted to do mainly small batches of 4x5 [1 gal.], I chose to make a smaller development tank [I only use gas burst for development] out of a Kodak 5x7 hard rubber tank [easy to drill holes in] and put my piping in the bottom. I've not found any sourcing problems with gas [found everywhere welding gases are sold].
What I did was get the large tank and a valve system which goes on top. Then I bought 100 ft. of small tubing from a woodworking place in New Mexico, along with a smaller step down value used by woodworkers re: air powered clamps. I step down the gas pressure to 25 psi at the main tank, run it through the tubing to my darkroom, and use the step down valve there to step it on down to 15 psi, which is the pressure used at induction into the timer. Works great.
Let me know if I can help further. I just don't understand why other LF photographers don't go this route. It solves so many problems.