Some systems have blowers that are easily removable with the squirrel cage coming out with it. If your car is like that, remove it and expect to find a nest, hair and string in, around and nearby the blower. Clean it out. If it's one of the cars where you have to essentially take out everything from the radiator to the gas tank just to look at the blower, then I don't know........live with the low flow?
Oh, I thought of one more thing that might help. Does your car have a cabin filter? Personally, I think these are the stupidest thing ever invented, but whatever. Remove that, gut it and then put it back in just to keep the area sealed. You might even find that this opens up the flow.