For magazines, like everyone else has said, go with the CMI mags...they are the best
currently made and current USGI (the older USGI from the Vietnam era producers were
the best ever made, but be careful there are a lot of counterfeits on the market and some are hard to tell apart from the real ones...if you're that interested send me a private message for advice, if just looking for good mags then buy the CMI ones, or the ones marked BRW or BRW S-1 - both are CMI, but from a much earlier production run and usually cheaper than the current CMI...CMI is the supplier of magazines to Springfield Armory
For scope mounts there are a lot of options out there, but i personally think the SEI mount is the best available:
http://www.smithenterprise.com/products03.03.html
Its not cheap, but is very very high quality...Just a lil FYI, you may have to have the mount professionally installed depending on the make of your M1A...some of the manufacturers over the years did not have specs like the scope mount bolt hole or the stripper clip guide 100% correct and you only notice it when you have a scope on the rifle and trying to hit distant targets.