My friend Mat and I put together Dallas and Cane uniforms a few years back.
A few observations...
The Dallas and Cane jackets appear to be the same base jacket.
Because of the odd buttons and large collars we thought they might be cut down British trench coats.
Both jackets have the compression lacing on the sleeves but Cane is missing the large web panels on the chest.
Dallas has gold wing insignia while Cane's has silver.
They both have the pink piping trim piping on the collars and epaulets which is also seen on the uniform shirts.
Thoughts on the Compression Lacing:
The compression lacing on the sleeves and chest of the jackets is the same as the lacing on the back of Ash's and Ripley's jumpsuits.
The lacing on Ripley's jumpsuit sleeves has been removed (probably to make it easier to roll up her sleeves or tie the sleeves around her waste).
My thinking is that they had several of these compression jumpsuits and used the back panels and sleeve lacing to jazz up the Dallas, Kane and Bret jackets.
Another reason I think this is that I've seen the same Ash/Ripley jumpsuits used in old 60's British sci fi films and Dr. Who episodes.
Our costumes:
Without access to British military surplus we did the best we could with suplies here in the states.
For the jackets we modded some old Nam era mechanics jumpsuits and made our own compression lacing.
We stenciled out the Nostromo lettering on the jacket backs and used silk screen ink for the lettering.
For the pants we bought two pair each of white painters pants and cut up the 2nd pair to make the extra pockets and knee pads.
The belts appear to be seat belts, almost certainly taken from the bombers that were purchased to build the sets and props in the film.
We simply used fastex buckles and made cover plates with the pips.
The shoes look like Kedds High tops but they've modded them by riveting small "D" rings through the lace holes.
My Dallas uniform is in storage but I'll retrieve it and post some pics.
If anyone from the UK can ID the actual jackets or jumpsuits please comment!