I'm based in the UK, so buying the Lee diffusers was straightforward. To get the Solux lamps I had to ask an american friend fly with a bunch of them. This was years ago.
The Lee diffusers are made of glass and are attached to the bulbs with a metal holder that wraps round the back of the bulbs (Lee sells these holders). The holder is low profile - it doesn't get in the way of inserting the bulb into the track fixture.