Evergreen Scale Models and Plastruct are the two main US producers of styrene sheet, rod, tube, and scale architectural shapes for modelers. Most hobby shops (and some game stores, but fewer than those who deal more generally in modeling) will have a selection from one of those two. Plastruct has a
list of distributors on their website that can help you find a local shop that carries their products, if there is one. Evergreen doesn't have a list displayed, but their website gives contact info to find local retailers:
Evergreen Scale Models products are available in hobby and art supply stores worldwide.
For a retailer near you, please contact us at 425-402-4918 or email to
info@evergreenscalemodels.com
Barring a local retailer, there are online options, as well. I've bought my small stash of styrene through Ebay sellers, but electronic storefronts (dedicated websites, as opposed to Ebay stores) for brick and mortar hobby shops and online hobby retailers like
HobbyLinc are also options.
As for tips, there isn't
too much to say (but I'll take my time saying it, as I'm wont to do

), considering how straightforward your intended project is - each respirator cartridge just takes two cuts and two dabs of glue. When cutting rod/tube, I recommend setting your blade atop the material, as close to perpendicular as possible, and rolling it back and forth while applying gentle downward pressure. The resulting cut has a nice, small chamfer to the edge and is generally straighter than what you get by simply chopping (it's an extension of the "score and snap" method of cutting styrene sheet, which avoids the distortion caused by the width of the blade passing through the material). Clear your workspace and try to cup your hand over the piece after you've got the cut started - the trimmed off bits tend to go flying if you aren't careful.