Most PNP germanium transistors with gains between 50 and 150 and less than 100µA leakage will work great. Some good ones in my experience have been:
- Soviet: MP20A/B, MP21A/D, GT115G, GT309A/B/G, GT310B
- Chinese: 3AX31B/C
- American: MA287, 2N404, 2N1305, 2N1307, 2N1309
That's hardly an exclusive list; lots of others work great, too.