The tire stores in our area tried their best to sell us the ST tire that gave them the highest profit margin as they didn't have Maxxis tires either which is common even in the US. Have a few buddies that are mechanics at both dealership and privately owned garages an they stated that any reputable tire store can attain whatever tire they want although it may take a few days.
Went to our local Discount Tire and Carlisle was the ST flavor of the month at the time, told them nope I want Maxxis which of course they didn't have in stock. Told them thanks but DiscountTireDirect.com had them with free shipping (there is a shipping fee to Canada) and lo and behold they said they could have them in a couple of days.
Discount Tire called the very next day and told me they had them and they were installed an hour later. I did use DiscountTireDirect.com on a prior set of Maxxis ST tires and they were delivered to my front door via UPS in three days, took them over to Discount Tire and they were balanced, installed, and warranted without issue.
The point being is if you really want the best ST tire currently available you can get them. If going up to the next load rating on the same size tire make sure your rims can handle the psi required to run your new ST tires at max psi as stated on the sidewall. Running ST tires much below the max psi will cause them to overheat which is why so many have catastrophic failure.
We have had good success with our Maxxis ST tires and our current set are 4 years old and have nearly 25K miles and still riding strong on our 10K# 32' TT. Will be looking at a new set soon and Maxxis is the only ST tire I'll go with. Quality heavy duty LT tires are a good option for the heavy rigs, but Maxxis makes a dependable ST tire that works well for rigs 10K# and under.