Your clinic should supply those. Always, it is considered part of your treatment, and the clinic is paid to have them for you. Ask them for an extra one if you need it, they should be able to provide an extra one here and there.
When I had my cath I preferred the "cloth" dressings to the tegaderm because I found that I developed horrid itching and a rash from the tegaderm. However, I used to perspire a fair bit at they gym and so the dressing would usually begin to peel off. They changed it almost every session (three times a week at that time) no problem and they gave me extra to do it in between if necessary.
I want to use Tegaderm over my chest cath so I can shower. Does the entire cath need to be covered or certain parts? And where can I get some (besides from a dialysis clinic)? CVS has some, but they aren't very big at all.
And they have a built in pad on them so they don't get the cath all sticky