If you plug in the tire size you're looking for in the link below (When it opens, you'll be asked to enter the Vehicle you are searching for - Don't).
https://www.discounttire.com/
Once the page opens look towards the top left and you'll see categories for Tires, Wheels, Accessories, etc. just Click on the down arrow to the right of 'Tires" and a drop down will appear - select 'Shop by Size'
Once you plug that info in It will produce all the Tire brands in that size... (on the left side of the page you have options to narrow your search farther by selecting Brand, Cost, Tire Category, etc.)
From there; just click on any Tire you are interested in (once the page opens scroll down to find the "Load Index' & using the chart above which Scalf77 supplied you can see what the MAX Load rating is).
***If you haven't already, you should take your Van to a Scale and have it weighed since you have a build out (at least get both front & rear axles since the load rating will need to accommodate the heaviest end - then also ADD weight to account for stuff like gallons of water & fuel if they are not currently full, Food, and stuff like accessories & clothing if not already in the Van, weight of the people traveling, etc... so you can 'guesstimate' what your loaded weight would actually be)