Vinyl Surface Mounting Block For Siding
If your question was where to get the contoured gasket that fits between the vent flange and the angled siding, you can fab. one using caulk or spray foam if you cannot find one contoured like your siding. It is best to use masking tape onto the siding across the top and down both sides of the vent and on the face edges of the vent. After the vent is mounted and secured to the siding, caulk the gaps with a matching color latex caulk. Smooth the perimeter of the vent caulked edges with a wet finger until you are satisfied with the look. After the caulk has firmed up, gently peal the tape up to reveal a crisp edge border around the vent edges. The more you mess with it at this stage the worse it will get. Without the tape, the edges will be uneven and feathered like all the novice nasty bathtub caulk jobs you see everywhere. If you use spray foam, tape a wider masked frame area and the face edges of the vent. After the foam has set, use a razor blade to trim off all of bulges and warts. The tape keeps the foam from staining the siding and the vent face and leaves a crisp edge. The foam leaves permanant stains on most materials and skin. The foam will darken to a baby poop color from sun exposure if not painted.