I have had Buds Brake & Wheel Parts in Bakersfield change out 2 welded on axles for me in the last 2 years.
The first was on 14' Lil Bigfoot
which required a frame modification and the second was on my 13" Scamp
Both axels included brakes
Axel and all for each was about half of just your labor to install a new axel.
They have been in business for years and work mostly on commercial trailers.
He should be able to order the axel for you.
If you want to give him a call the number is 661 322 7061.
I very seldom recommend any business but this one has done an excellent job for me at a more than reasonable price twice.
It might pay you to drive 100 miles or so.