This time, it was. I browsed around inside briefly; they sell daruma dolls and a few other handicrafts, a few variations of rice crackers, and some clothing. I almost bought a hat that said "Born in Koshigaya" but decided against it.
ガーヤちゃん), the Koshigaya mascot. He is a duck with leeks in a pot. He's not really being cooked, despite his sad appearance on this patch. The pot is actually more like a pair of pants, and the leeks serve as a sort of tail. I think. This is the first time I've seen the mascot, and I had to have a little souvenir of the town I've called home for three years running now.
As I mentioned earlier, the store has senbei. I think every town has a "local" senbei, and nearby Soka City is well-known for its senbei. Senbei is a rice cracker, usually seasoned with soy sauce.
Other things I saw in the store related to Koshigaya's local trades include wooden boxes, daruma and other dolls, and a couple different drinks. Additionally, Koshigaya has a small agricultural market and is known for its leeks and chestnuts. The duck comes into play because there is a former hunting ground in northern Koshigaya which is now a park of sorts. Or it might still be a hunting ground.
The store, called the Koshigaya Bussan Exhibition Hall (越谷市物産展示場), is open 10:00-19:00, closed Mondays or the next day if Monday is a holiday. There is a large case of local goods on display, and smaller items are available for purchase around the rest of the shop.
From Koshigaya Station's ticket gates, turn right, then go left to follow the train tracks north. The entrance is at the end of the small shopping center, past McDonalds.