Where to Look
As with all used cars, Auto Trader and other classified car magazines are a good place to start your search. Since these aren't collector cars and most served daily driving duties, don't expect a low-mileage garage queen. Many LT1 Camaros on the used market have between 100,000 and 150,000 miles on the clock. That shouldn't be a turnoff, however, since the LT1 is essentially an updated spin-off of a traditional small-block Chevy and therefore extremely durable. Likewise, shopping at the right places will save you loads of money compared with dealership prices, so you won't go broke buying replacement parts should something go wrong.
Online shopping is a powerful tool, and some of the best places to find leads these days are on message boards. For LT1 cars, Camaroz28.com is an excellent resource for both online classifieds and detailed tech info. Since like-minded enthusiasts take much better care of their cars than the average driver, vehicles listed on message boards are less likely to be turds. The downside is that enthusiasts sometimes have difficulty distinguishing between sentimental value and true market value, but that's where your negotiating skills come in. Classified ads and pricing reports from Kelley Blue Book (kbb.com) and Edmunds.com will give you an idea of what is and isn't a fair asking price. Auction sites like eBay are worth a look as well, but use common sense before bidding, as pictures tend to hide imperfections. Although Carfax reports aren't infallible, they are worth purchasing for at least some insight into a vehicle's history.
Common Problems
Opti-Spark: The optical ignition system (Opti-Spark for short) affords extremely precise control of ignition timing from cylinder to cylinder. Unfortunately, it's extremely intolerant of moisture yet positioned directly behind the water pump. New factory replacements can be had for $250 or less from GM wholesalers, or the stock unit can be rebuilt with cap and rotor kits from ACCEL, MSD, and Summit for $100-$150. ACCEL and MSD also offer entire aftermarket Opti-Spark replacement units with improved internal components. Unless the Opti-Spark has recently been replaced in the vehicle you're looking to purchase, expect to fix it.
Intake leaks: What often appears to be a rear main seal leak is most likely a leaky intake manifold. Removing the intake and applying a liberal dose of high-temp RTV on the front and rear of the block should sufficiently seal the manifold from future leaks.
Driveshaft vibrations: The steel 2.75-inch driveshaft in LT1 Camaros often vibrate on the freeway, most noticeably at speeds above 80 mph. Trying to rebalance it at a driveline shop is a crapshoot. The cheapest fix is scouring junkyards or message boards for a 3-inch aluminum drivehaft out of an LS1 Camaro or a 2.75-inch aluminum unit out of a third-gen 1LE F-body for $150-$250. If that doesn't pan out, aftermarket units from Denny's Driveshafts or Inland Empire Driveline will set you back $300-$400.
Misc: Minor mechanical bits also prone to failure are the transmission mount and power-window motors. Energy Suspension and Prothane both offer urethane replacement mounts for less than $30, and the swap takes less than 30 minutes. The power-window motor replacement procedure is a bit more involved, but the parts can be purchased from your local auto parts store for less than $100.