That product isnt a slide pot. Its adjusted by the knob on the end and that moves the white slider along to indicate its location, similar to the red line that moves on an old radio tuning dial. Its probably very small too, a trimmer tends to be a PCB mounted pot that is not frequently adjusted, just set up once or re-calibrated every so often.
Try edlieelectronics.com . I got an assortment of them that is supposed to be 15 various lengths and ohmages for $2.50 but they all had about 2" stroke and about 10K ohms. You could put 2 or 3 in series. If they don't have them now, let me know. I have more than i need. (no charge)