Wheelchair

My son has had a major buggy but unfortunately it has now been condemned and we are on the waiting list (apparently the urgent one!) waiting for a wheelchair. However, although the word "urgent" has been used we are still waiting and it could be an even longer wait until we get an appointment through!! My son can walk but not very far so we rely on a chair for him to get around. The Wheelchair Services cannot help with a replacement in the meantime so it is very difficult to get out and about, especially to appointments in London. Can anybody recommend anywhere that will offer a temporary wheelchair in the meantime? The Wheelchair Services do not have any chairs we can borrow! Any help would be appreciated! Thank you!