I know you said you don't have much time, but when I was at the Grenelle store late march (16 Rue de Grenelle) they had a lot of trapezes (at least 5-6, because that was how many I was shown, but probably more) so you might have better luck there. Also, it's actually not that far away from where you are living, (I would estimate maybe a 15minute trip or less but someone who knows Paris better correct me!).