Hellertown PD should be on Northampton County South PD channels. Station number should be 13.
South 1 502.38750
South 1 500.41250
If you are looking for private frequencies, I don't know. But you could try these listed in the FCC records for Hellertown Borough. These are listed as PW, some of the police used public works frequencies in the past from time to time.
154.7850
460.5625