Cokin compatible filters

I have a Cokin A series filter system. I like the concept of the system since it allows me to use the same filters for all of the lenses in my 35mm and digital SLRs as well as my large format cameras, but there are a few problems with it. The biggest problem is that Cokin doesn't make a true ND filter. Theirs have a color tint that seems to vary from one production run to the next. I've seen them described as anywhere from gray to purple. This wouldn't be a problem for when I'm shooting film since I usually shoot B&W, but as a filmmaker with a DSLR, it isn't appropriate for me.

I'm also not a fan of plastic. The plastic seems too soft. My yellow filter developed a groove down the center from the lip of the holder within the first few months. I would like some glass or harder plastic filters.

Does anyone make glass filters that fit the A series filter holders? My searches so far have been unproductive.

Did you check Lee filters? I'm getting a Cokin filter set myself - holder, adapter rings, one ND grad - and was wondering if I can upgrade the actual filter to a Lee one, still using the cheapo-ish cokin filters.

From what I've seen so far, Lee seems to only make 100mm square filters. That won't fit in the A series holder. I just discovered Kood. They make A size filters. Has anyone here had any experience with them?