Taking out you Blythe's original eye chips is a fairly easy process. All you need is a hot glue gun, or candle, and a glue stick. For a full tutorial I suggest visiting Blythe Life: Changing Eye Chips.
As for the clear chips themselves you can't go wrong with 'Cool Cat' Clear 'Custom Flat' Eye Chips.
After a with I tried buying 14mm clear domes or cabochons from Etsy sellers. You could get many sets of domes for a fraction of the price. I tried an acrylic one with a sticker back. It was a perfect fit and worked great. However some required a touch of sanding to make them fit. I assume this is due to the eye sockets themselves being slightly irregular. On that bad side the domes I purchased turned yellow after about a year. That was really sad for me. They were still usable with brown or orange chips, but not ideal. I'm sure this was just bad luck on my part, I would definitely try my luck again buying these domes from a different source, just because of the extreme savings in cost from buying the Cool Cat eye chips.
Bellow are sampling of the images I have modified and created to go behind the clear eye chips. You can find collage sheets for realistic eyes here and anime eyes here.
As for how to make the custome eyes, you simply print the page, cut out the circle and place the paper into the eye socket and the dome snaps on top. No glue needed.