Buying a bundle of lathe board (4 footers) and then cutting you own
wood vee spreaders provides a custom range of lengths for little money.
Nail point spreaders are readily made if you purchase the double-ended brad points made for this purpose. And then there's Wilson Orchard & Vineyard Supply selling both versions in bundles of 100.
A bulk source for shorter-sized
red plastic spreaders has fallen off my radar. Stark Brothers sells
these in packages of 10; choose from 6, 9, 1nd 12 inch lengths. But these would be pricey for a commercial grower. MP6 in Traverse City, Michigan manufactures Twiggeeze spreaders ... you can get twice again the range of lengths in full box quantities if you open a commercial account.
Zinc-coated vee spreaders by Treeform in Ontario are carried by a number of distributors.
High density training calls for less rigid options for green shoots with trellis/ stake tie points. Peach Ridge Orchard Supply offers a range of rubber bands, toothpicks, clothes pins and so forth, as do others. Light gauge wire is in this class.
Lost Nation OrchardZone 4b in New Hampshire