I know there are these two questions already (https://judaism.stackexchange.com/questions/36703/trying-to-get-shmita-year-dates-without-a-headache) and (When is the next shmita year (as of 5772)?); however, they don't appear to provide either a table of date spans or links to one or a general formula for determining the conversion to Gregorian/Western/Christian calendar dates. I couldn't find an exact table of dates only years with a few Google searches.
Since the Jewish year begins on 1 Tishrei and ends on 29 Elul, your question is essentially to translate 1 Tishrei and 29 Elul of every Shmita year into Gregorian.
The Shmita years are those divisible by 7. Since 1900 these years have been: 5663, 5670, 5677, 5684, 5691, 5698, 5705, 5712, 5719, 5726, 5733, 5740, 5747, 5754, 5761, 5768, and 5775 (which began today).
So for each of these, you want to find the Gregorian date for 1 Tishrei and 29 Elul. You can do this using any of a variety of calendar conversion apps and websites, such as http://www.hebcal.com/converter/.
For example, the first Shmita year in the 20th century was 5663, which spanned from 1 Tishrei 5663 = 2 October 1902 to 29 Elul 5663 = 29 September 1903.