Not enough defrost to windshield

[Omicronmike]

My 88 LE tends to fog up during the winter when snowing out because not enough air is blowing through the vents at the front windshield. If the cables are adjusted to fix that, then there is not enough air sent to the floor and mid areas when switched to AC. There is plenty of heat, the problem seems to be something to do with perhaps the cables stretched or the air valves not wanting to open up fully when modes are switched. The cables are no longer available from Toyota. I have never taken the dash fully apart (and hope to avoid that). What is the best way to fix this? Any way to avoid taking the entire dash apart?