If you're looking to get access past loch Katrine it's a bit difficult, as previous post says contact DOC.
If you want access past the loch for fishing you may be OK, however if fishing is what you're up to i have this for sale which will give you access from loch katrine, through the channel from the loch through to lake Sumner, then upstream i've had it as far as the swing bridge which is where the old number 2 hut was before it was burnt down.
The rd to the loch is an easy tow in a std 4x4.
cheers
Tim
http://www.trademe.co.nz/Browse/Listing ... =564166112