Where do one find these? and have anyone tried them?

I would love to try it as i heard it can help astma.

I dont know about lung expansion, but you can aid lung efficiency by simply practising holding your breath throughout the day. Say, hold your breath for 1 minute every time you recieve a phone call/go to the toilet/whatever. Once you can do this try moving up to 1min30. etc etc. It is easy to do these regularly as there is no need for equipment.

exhale against resistance.

blowing up balloons, rubber surgical gloves, latex condoms , and ultimately, rubber ice bags,
until they burst.

P.S. wear googles.

Actually, asthma still can over-ride these efforts as the bronchial tubes become constricted, versus lack of lung capacity.
Two different entities in play.

Swim. Take a big a breath as possible and swim underwater for as long as you can. Will increase volume, and the length of time you can go without air.

I also do squats. For some reason, maybe having to be full of air at the bottom, to come back up, my lung capacity increased greatly.

Learn the harmonica. No joke, it's reasonably entertaining and you'll get better at breathing. Plus chicks dig musicians, even asthmatic ones.

You talking about a breathing resistance exerciser?

http://www.expand-a-lung.com, is the first one I found on google.

dumbell pull overs, and dumbell over head extention, theirs a squat method where u put like 100 pounds on the bar, go down , breath heavy 3 times, lift up repeat 10x for few sets ive heard. not 100% tho

Or you could try talking to the person on the other end.

Seriously though, start playing a wind instrument.