Brass screening can be found at plumbing supply houses. Plastic screening can be found at fabric stores or craft shops. Both are available in various sized mesh. Also look at filtering medium used in air purifiers. Some use a fine plastic mesh pre-screen.

Keep an eye on the packaging of products you use. I found a really great source of fine (plastic) mesh that was a 'holder' for a doll accessory my grand daughter had. Couple careful cuts along the seam and it opened up into a sheet about ten inches square. It now resides in my supplies stash.

Detail master used to sell some.