Using Avon Roadriders front and back, excellent sticky tyres!
Roadrunners are going to be very old now, if you do find one check the date stamp on the side of it for the month and year it was made?
The tyre itself will have a four-digit age code on the sidewall, this will tell you the week number (0-52) and the last two numbers of the year of manufacture, in this example week 40, and 09 (2009).
Anything obviously cracked, perished or rock-hard will by now have the grip properties of mahogany / old wellies and is best left to be binned...
Tyres are the only thing stopping your bike scraping down the road, best buy good ones, eh...