Letters to Kusum and Kapil
Osho wrote many letters in Hindi to Ma Kusum Bharti and her husband Kapil, then of Ludhiana. All but a few were published in Prem Ke Swar (प्रेम के स्वर) and in Ghoonghat Ke Pat Khol (घूंघट के पट खोल). The wiki has images of all the published in PKS, plus two more that have not been published as far as we know, plus one in English, published in The Gateless Gate, so 30 in all. As well, we have a few envelope images.
Additionally, some letters to Kusum were published in Prem Ke Phool (प्रेम के फूल), but we have no images of them.