Ok... you can create your own image easily..
Make a button yourself, publish it to your server.
Then go into paypal and create the subscription.... then where it asks you what button you want it gives you a chance to add your own image by giving them the url.
so for example if you name and save your image as monthly_payment.jpg
You place the image on your server, then give paypal the url
http://www.whateveryoursiteiscalled....ly_payment.jpg