A 2.048GHz frequency Source

As above,

is there any way to get this frequency directly? seems to me that i need to use VCO. Is there a simpler way?

You could use a frequency synthesizer which will be the most accurate option if you need to use the source in multiple places. But the short answer is yes VCO or synthesizer is your best option.

You don't mention what it's for?, but the conventional way is to multiply up from a lower frequency crystal - I seem to be recommending them a lot recently?, but the ARRL and RSGB handbooks would be good sources of suitable circuits.