Well, you can still buy silicone/silicate inhibitor coolant in several forms, but you have to look harder and harder for it. Look for "heavy duty" or "diesel" coolants and then check the MSDS or product spec sheets for silicate inhibitors- this is the old "green" Prestone type formula.
If you want to make life easier, it appears that G-05 (the coolant Ford and Chrysler have standardized on) is just fine in older vehicles. Its a hybrid coolant, using both conventional inhibitors and organic-acid technology (OAT) inhibitors, and is thus categorized as a "HOAT" inhibitor package. Its very different from Dex-Cool which is an OAT inhibitor package, and is deadly to pretty much everything you put it in except a few GM cars.
Prestone "all makes" looks like its also a HOAT coolant, and so should be about equivalent to G-05. But given how vague Prestone is about what's really in there, I'd be tempted to go with Zerex's clearly-labelled G-05 coolant.