I really like the support the people down at Courtesy Nissan provide http://www.courtesyparts.com/
The oil pressure sending unit depends on whether you have the gauge or light but check with Courtesy on that.
The front left axle can be sourced locally in Des Moines from Hummel's Nissan or a quality remanufacturer/rebuilder.
As for the lower control arms, are they required to be replaced because of the bushings or are they physically damaged? I ask because if the bushings are bad you can use Whiteline (part no. KCA 303) or Energy Suspension (part no. 7.3111) urethane replacement. It is some work to get the old bushing off but well worth the trouble since the bushings are only about $60 for both replacement bushings
There are two belts for the 93-97 Altimas. One for the A/C and one for the PS Alt. and Water Pump. I would replace both of them.
When I buy parts online,I usually go to yahoo and search for my part.
Foe example:" Nissan altima fuel filter". It gives me a lot of web sites so you can choose the best quality and price. If you have no idea what your part looks like and what ti does,there is a picture and some times a little of explanation You can also use www.autozone.com and other autopart store web sites.