Hi,
Try visiting any of those:
- at Wioślarska street, near the crossing with Ludna st. The shop is between the Wioślarska and Vistula
- at Wał Międzyszyński I guess 377, there are several shops with such things, also on the Vistula side of the street.
- Spójnia, at Wybrzeże Gdyńskie, under the Warsaw Citadel, there are several diving and motorboat shops. There has been windsurfing shop for some time, but as far as I'm concerned it got closed. But maybe you're gonna find something interesting in diving shops
Those 3 mentioned above are three most popular places. I'm almost 100% sure there are more shops, but I know only those 3 locations.
If you had problems with finding them, write me or directly here on the forum, and I'll try to help you.
See U on water,
Patryk