Played for a good 80+ hours overall, the character I have at the moment is level 59, haven't seen any 'boots of muffle' that I can disenchant.

I understand mostly its random loot, but every other enchant has a sure location, e.g. fiery soul trap. Does anyone know any sure locations?

In my PS3 game, I found them in random loot but in my PC game I never did. I got them from a merchant. I'm not positive from whom but I was always checking the Khajiit caravans for enchanted items and I was spending a lot of time in Windhelm then. Maybe it was at the used goods guy in Windhelm? Good luck. I disenchanted the item and then put the enchantment on my one lb boots.

:tes:

I found some randomly on one of my other characters
but I also recently recieved a pair on a quest

It can be purchased from Calcelmo, Drevis Neloren, Falion, Farengar Secret-Fire, Madena, Sybille Stentor, Wuunferth the Unliving and Wylandriah at around level 20-25

EDIT: Oh sorry enchantment. Yes by luck or through the thieves guild.

Bought a pair in Whiterun to begin with, almost cleaned me out at the time and I couldn't disenchant at the time but thought they would come in handy later.
Same with a helmet with water breathing ability.
Had a few different ones pop up as random loot now and again though.

Saw a bow of paralysing for sale. "Bound to be more. Won't get it just now." Bugger!

I've seen them only once (outside of uniques), at some blacksmith. I think it was the guy at Solitude, but I am sure it was purely random.