[sneeker418]

I am planning on building a 150 inch screen and then painting it with an ALR paint. Problem is I can't seem to find any blackout in the size that I want here in Canada. Any suggestions from people who have done this on where I can get this material or any other suggestions on how to go about this.

 

[MississippiMan]

You should use Carl's Flexi-White material...found HERE

It is easier to work with, has a much smoother surface that accepts paint better, (less Fuzzies) and only costs a very small amount more per yard. ($11.95 vs $8.95 per Yd.)
Carl's ships to CA addresses. I don't know of a single CA outlet for either a comparable Screen material or Black Out Cloth in the sizes you want so ya gotta do what ya gotta do.

You might want to scale back a very few inches to 144" diagonal so as to keep in the closest lower tier of pricing.

Flexi stretches well, but using the 144" size to fit a 150" Frame might be "stretching" it a bit much.