Agree with the previous answers and definitely suggest carrying treats with you. The biggest thing is training the "Look" command or "Attention" command or whatever you want to call it. If you train that inside first, sometimes you can get the dog's attention on the treat and then give them the treat if they remain calm. If they lose it because the skate boarder got too close, then I just walk the other way and they don't get the treat. As has been noted, it takes a long time for this to change the behavior permanently, but usually it does help at least a little in the short term.

There is also Pet Flow that sometimes does bulk ordering. You can also order some things through Amazon and put it on a schedule so it gets shipped to you every 2 weeks or so. A lot of their health treats and Nylabones are way less expensive than other places.