The Taronga Road Riders is a series of eight books by American author Toy Martin. The series is set in Australia, and features the Pokey Creek Pony Club. Toy Martin seems a force to be recognised with: when she was just 22, she had already been an Olympic speed skater. She migrated to Australia, and represented them in orienteering (about which she has also written books). Riding was a later accomplishment for her, but her two children were keen riders, and she became very active in her local pony club.
Finding the books
Alas the Taronga Road Riders series is very hard to find. Even in their native Australia they are uncommon. You might like to try ebay Australia for copies.
Links and sources
Many, many thanks to Danyele for all her help with this series. Almost all the information here comes from her, and I am extremely grateful!