I recently bought 50 of the 39mm direct fit air-tites sold by JP's Corner and fulfilled by Amazon. Most of their products are not available with Prime on Amazon, but this one was and it saved me a bunch not having to pay for shipping. Their non-Prime option is also still free shipping. Not as helpful if you only need one/a few, but if you're starting a collection and know you're going to use them anyway may as well get a bunch!