I purchased the gas struts here:
1224 York Road, Saint Davids, ON L0S 1P0
(905) 262-4518 () · niagaratrailers.com
I tried to get them at an Auto Parts store but they only had them by Part Number for specific cars and trucks, and the struts did not have the rating on them.
I'd just got my new trailer and was on a shakedown trip so I tried Niagara Trailers who were near the campground. They had a good selection of gas struts and they were grouped by length and lb rating. I had the original strut with me (it was marked as 80lb) so we didn't need to measure it. I don't recall the brand, but perhaps you could contact the dealer.
My trailer is in a storage facility so I won't be accessing it until late December when we head south.