data copying between sheets

Hi guys, trying to copy some data in a spreadsheet ive made, and add some data automatically. shouldnt be too hard but not quite got my head around it.

Basically i have 2 columns of data in multiple worksheets which i wish to copy into one column on another sheet.

Ideally i want to be able to click a button and have all the data compile with the item number and serial number into sheet "compile" no matter how many sheets i have (my current macro copys the sheets with a sheet prefix onto it, ive left 31 and 32 there) automatically. Ive edited compile with one sheet of data (note i just copied 31 to 32 - normally all data would be different, not a straight copy) to show what i am trying to achieve. the 17000 will stay the same no matter what, so i just used an IF function there. Basically the part im having issues understanding is how to copy data to the next blank space in the work book, as it wont always be full of data.

At the end of getting this part working i will set it up to automatically compile into a seperate work book as a csv comma delimited to upload to a database for stocktaking purposes - but i just want to get the basic copying working first.

thanks guys