Radars are so difficult to obtain as to be unrealistic to collect. Euro banknotes have 11 digits, not counting the country prefix letter, The final digit is a check digit stepping by nine for sequential notes (see another thread in this category). With 10 digits, radars would occur every 10000 notes, where US and Canadian radars occur every 1000 notes. If the check digit is included, I think the frequency is one per 900000 notes.
With respect to sources, unless you have access to one of the EU national banks, eBay or EU dealers are the best source. Expect to pay a premium over the exchange rate, maybe US$2.00/euro. This can be substantial for the higher values. Try putting together a country set: 11 countries (I don't think Luxembourg, 'R', has issued banknotes), with more countries coming shortly, times 7 values, times 2 ECB President signatures. Then there's the printer codes .....
blumax