Have any suggestions of who to call to get a complete set of dual wheeled axles?

The current brakes are hydraulic and want to replace with electric over hydraulic with stainless steel discs. I beleive it will be easier to replace the whole 9 yards.

There is Dexter Axles and Quality Trailer Parts.Both of them have warehouses somewhere in Florida.
I'm not sure if stainless disc is available.Heat rejection on that size disc may be a problem.If SS disc is not available,part of it may be because of disc warp.
I'm sure you know,the vehicle brake control must match the electronics in the servo, electric/hydraulic system.
Because of the distance to the axles,the brake line should be SS .250 ID,then 3/16 ID from the front axle to the rear axle.Any part of the line that moves should be braided SS, Teflon lined hose with banjo fittings.Also, from the control system to the SS hard line....Cost,$650---700 material.
Subject to the control system chosen,the control output fitting should be drilled and tapped to accept a 5/16 OD fitting on the SS flex hose.The standard little orifice is probably not large enough.
There may be room for argument with the wheel seals.However,if you dunk the bearings, it is probably safest to use grease seals instead of oil bath.The clear oil bath axle cap will allow one to notice if water has entered the grease.
Personally,the axle spacing is as minimum as possible.Because,it is easier to maintain alignment and reduces tire scrubbing,when turning.
Further,close spacing seems to have less flat tires.
Because,of the suspension width vs;axle length,the axle tube wall thickness will probably be for a 10,000# axle.That puts pricing in an up charge over a 9,000# axle.Then,if one wants to be creative,order a set of 20,000#bearings instead of 9 or 10,000#......the rolling resistance will make it feel like the trailer is pushing the tow vehicle up the hill.
However,the brake shouldn't have ANY problem stopping.
Last,when the axles are aligned,one may want the trailer to pull slightly towards the crown of the road.

Thanks CCanDO.

The Menace,You are welcome.
Let us know what you decide to do and how it works.
If I can help in any way,let me know.