HiA lot of guitars appear to be classical guitars at first view - the open head stock often fools most people!
If you can't find details of the actual guitar, I use the following guide lines,
Are the winders(tuners)centers made of metal (metal centres tend to imply steel strung - wider plastic/bone etc tend to be nylon strung)
Has the guitar a Tail piece? most nylon strung guitars have a fixed bridge (without 'pins')
Is the neck wide or narrow (wide implies nylon - narrow steel)
Is the neck curved or straight (across its width) - curved = steel Flat = nylon.
Fixed bridge with pins usually goes with a steel strung guitar - a straight through bridge with fancy inlay - not just dots - tends toward nylon.
Of course there are several other variations - most nylon strung classical guitar have 12 frets not he now normal 14 frets - although early steel strung (parlour etc) also had 12 frets.
The best bet is to check through early books - guitar history or this site (I'm sure many more people will add their comments) and trace the exact model as lots of damage can be caused by adding the wrong kind of strings - worse being steel strings on nylon guitar but also the other way around (Nylon & Steel strings always worry me!)
All the best in your search..
& Merry Xmas
Pete (Clansfolk) UK