This topic does come up from time to time.
The first thing as that clothes made for cycling are not necessary for most folks. If you wear padded shorts or underwear, you obviously want to be able to get those, but otherwise, most clothes made for active use (hiking, climbing, skiing, etc.) are useable for cycling. The one possible problem with using stuff that isn't made for cycling, is that sometime tops & jackets aren't long enough to cover the lower back on a bike. Fashion has changed in the last few years, though, and jackets and shirts alike, tend to be a little longer, especially at the back. So, you might try places like TK Maxx, the warehouse type outfitters for stuff that can be used on the bike.
Also, see these previous threads for ideas, though some of the links on them are no longer validviewtopic.php?f=1&t=69284&p=594876viewtopic.php?f=1&t=77351&p=717901
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom