The digital frequency display you usually see on tuners is made possible because frequency tuning is done using a PLL and a digital divider circuit. The division factor is displayed through a table, which shows you the frequency.
From what I gather you're using a varicap/potentiometer for tuning. You might try using an A/D converter on the potentiometer and display the digitized value through a table. It won't be perfect, but you'd have digits.