Don't be too convinced that a store-bought antenna is going to work any better. I hope that it does for you, but the home-built ones can work very well in comparison.
I'd suggest that you look for one that is designed for VHF and UHF, given those trouble stations. Most of the newer "digital" antennas are geared towards UHF because that's where most of the digital broadcasts are (or, at least, were) located. That doesn't mean that they won't work for VHF, but the smaller indoor antennas might not work well over the larger frequency range because of the trade offs in keeping them small while tuning them for a certain frequency band. My outdoor antenna was labelled as "UHF" but pulls in the upper end of VHF very well, but it's also pretty large.