In Numbers, you can not lock a range of cells within a table. However, you can move (or copy) those cells to another table and lock that table. The new table can be small (just the range of cells that you want to keep separate). You can hide that table on another Sheet if you wish.
Menu > Table > Lock
Make sure that the locked table has no formulas that link its values back to any other table. Formulas will still update the locked table.
Have a look at Menu > Paste Values to paste values (not formulas) into the new table before locking it.
The Numbers User Guide is a useful read. Download it from the Help Menu in Numbers.
I've never used a spreadsheet which did not allow locking cells. My spreadsheet has a number of individual (and scattered) cells that need to be open but it is too easy to accidentally put info in a cell that must not be changed and mess up the entire speadsheet. I need to be able to lock the entire sheet and then unlock the specific cells which have info changed all the time.
Major fail for Numbers
The generaly solution was to place user input in one table, then place calculations in a separate, locked, table.
Great advice for using any spreadsheet, not just Numbers! Keep input and calculations in separate places as much as possible. The table-centric design of Numbers makes segregation particularly convenient.