You talk like you have never seen the datasheet of the LM338. Datasheets have all the spec's and most application circuits.
The LM338 minimum output voltage is about 1.2V but of you add a -1.2V supply it will go down to about 0V.
Its output is guaranteed to go as high as 5A but two in parallel with an opamp as shown in the datasheet can provide more current.