I think that what you describe could be implemented with a simple loop. So make a vector of radii that you want to evaluate, set up a for loop that goes through the radii values, calculates p, calls your stokes function, and saves the results. Once you exit the loop you extract your velocity component and plot it agains the radius.
What are the dimensions of the variable v, that is returned by StokesletVelocity?
For illustrative purposes I will assume it is 3 by 1.
Then you could do something like this
radius = 0.2:0.2:10
p = [0.282 0 0.959]
numRadius = length(radius);
V = zeros(3,numRadius);
for k = 1:numRadius
p = radius(k)*p;
V(:,k) = StokesletVelocity(N,sing,p,Kn,f);
You may have to tweak the above slightly, as there are aspects of your problem that I couldn't fully understand from your description. Hopefully this gets you close enough that you can adapt it from here.