Quite an old post but I thought I would add some detail because I just had to sort some new pads for mine.
There are a few different models of Shimano pads. The G series are NOT the right ones. An internet search may lead to to a review of these brakes which incorrectly says the pads are G series. It leads to this post as well.
If you are walking into
Evans (I mean a London Road should be ridden in London right !) , then the Aztec PBA0093 SHIMANO FLAT MOUNT pads will fit. However, when you do fit them I found I needed to remove the metal heat sink/cage because otherwise there is not enough room for the disc. I am sure I can put the nice cage back later after some pad wear. But this tells me the original pads just didn't have much pad material or had a super thin backing plate.
I have also ordered some
EBC CFA734. These have arrived now and they look the right size. I see there is a lot of pad material and I am expecting the same problem with that metal shield needing to be removed.
When searching for pads you can search for Shimano RS405, Shimano RS505, or R9170 for example. This is the compatibility list for the PBA0093 for example:
GRX BR-RX400
GRX BR-RX810
Dura Ace BR-R9170
Ultegra BR-R8070
BR-RS805/BR-RS505
BR-RS405
BR-RS305
Hope this helps others.
PS. These brakes days are numbered. It's just the components to switch to hydraulic are currently over priced. Everyone seems to say rever havet are better than TRP and this implies perhaps they are good brakes. They are not, they have the stopping power of a slice of cheese. They aren't a patch on the hydraulic discs on my other bikes. Adjusting the front brake is a constant hobby. If you have SRAM Apex double tap then you will find you are constantly rescuing the double tap lever from being stuck against the bars because the brake lever travel is so far before any decent bite. The hydraulics on my other bikes are zero hassle, and they bite like hell. So yes replace the pads to keep the brakes serviceable whilst you save up for the new APEX AXS levers + calipers + a shiny new Apex AXS derailleur. Think of the safety improvement.
PPS. having tried to match the pads I also realise how small they are compared to other pads, like the G series. These pads are teeny tiny. This will be another reason why they don't bite as well just haven't got the surface area compared to an up to date Shimano or Sram caliper.