Tried to reply to your post but it's too old.

We have a few sacks of the Methocell F4M and it is the grade that's difficult to mix. It just clumps up as you sprinkle it on the water. You need to kind of mix a small quantity of water and the powder together into a paste and then dilute it down.

For those in the UK we have this on ebay at the moment along with some carboxy methyl cellulose at £29.99 per 1.9kg

Www.thegungeshop.com