Here is the 464 Manual scanned and converted to PDF files then zipped. The contents of this manual are copyright Amstrad PLC & Locomotive Software.
If you're just after the Basic reference then you want Chapter 8 and unless you're a complete newbie or have totally forgotten how to use a CPC you can skip the Foundation bits.

None of the files have been Intro & Contents (212kb)
Foundation 1 (566kb)
Foundation 2 (707kb)
Foundation 3 (858kb)
Chapter 1 (771kb)
Chapter 2 (372kb)
Chapter 3 (288kb)
Chapter 4 (779kb)
Chapter 5 (419kb)
Chapter 6 (378kb)
Chapter 7 (163kb)
Chapter 8 (2156kb)
Chapter 9 (192kb)
Chapter 10 (142kb)
Appendix 1 (227kb)
Appendix 2 (267kb)
Appendix 3 (1114kb)
Appendix 4 (278kb)
Appendix 5 (148kb)
Appendix 6 (151kb)
Appendix 7 (229kb)
Appendix 8 (186kb)