Description for plastic piece to cover cill

Our bungalow has these infilled sections beneath the windows where the wall stops and is replaced by a single sheet of something (timber, plasterboard ?) It's sort of pebbledashed on the outside, and at the bottom is a wooden cill, which looks tatty. I guess it's got a similar profile to a door threshold.
Not being a fan of painting, and having already got uPVC windows, and fascia, I'mm looking for something to clad the wood in, anybody know what sort of profile, or shape I should be looking for ? A quick gander at MasterPlastics doesn't throw up anything apparent ...
ASCII art profile ....
| | | | (pebbledash) | | | ---------- \ \ <- wooden cill/threshold \
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