hopefully this reply is not too late but the texts you are looking for are in tables STXH, STXL, STXB. The ID’s for the text types are in table TTXIT and these are as follows:
MATERIAL BEST Purchase order text
MATERIAL GRUN Basic data text
MATERIAL IVER Internal note
MATERIAL PRUE Inspection text
MVKE 0001 Sales text
You will have to use function modules to read the texts since these are cluster tables, i.e. text is stored in compressed format.
Hope it helps, AM