I am not aware of anyone offering any Amphipods (Gammarus) for sale other than some biologic supply houses that sell individuals for study and bioassay. $1 to $5 each will cost the moon to establish a population.
One other species that comes to mind would be Hyallela Azteca.
They are considerably smaller less than 7mm but, they are much more adapatable to climatic changes in their environment.
They can even be found living in the sulfur rich waters of the hot springs in CO at temperatures above 35C.
They are native throughout the world and could likely be caught in the area of each project. Except where (again) chemical contamination is a problem.
As for the true Freshwater Shrimp they can be caught using a lift net but you need to place a ball of bait (fish or blood meal, Aquamax may also do) in the center of the net and leave it for several hours. to allow the shrimp to find and begin eating.
One shrimp will attract more and more. Lift the net slowly to avoid startling them off the net and dump into a bucket or cooler with water and reset the net.
This method also works with crayfish.
The publication of my papers will be through the University of MN Sea Grant Duluth, MN.
I also have a paper comming out about the design and construction of an Riverine Spawning system for River Minnows.
This is in effect an artificial river that I invented 10 years ago here at my hatchery in MN. It was necessary due to heavy harvest pressure from the bait industry here of the Hornyhead (Redtail) Chub. Now with the ivasive species and VHS virus it may be the salvation of the bait industry in MN and elsewhere.
Barry