Scarce in all grades, R2.7.
The 1900 Dime is a very common coin that can be found with ease in all grades up to and including MS64. In MS65 and better grades, the population dips way down, but even those grades appear on the market frequently. In MS67, this date becomes extremely rare. The best example is a single PCGS MS67+ in the Lilly Nicole Collection.
The PCGS CoinFacts Condition Census for this date contains a minimum of MS65 and better coins, indicating the great conditions in which the 1900 Dimes have survived. The reader will note that virtually all of the top-end examples sport colorful toning and superb eye appeal.