Hi Sharon
The e-visa is obtained from the Indian Government website https://indianvisaonline.gov.in/evisa/tvoa.html
There are agencies which will get you the visa but you will end up paying much more if you go with them. As long as you read the instructions and work through all the questions carefully you shouldn't have a problem doing it yourself. You need a square photo and info page of your passport which have to be a certain size. There is also advice on the booking confirmation from Riviera which you will need.
I didn't have a problem getting mine.
Good luck
Helen