Is there anywhere I can find big and tall stores in Jinan?

I have no idea what kind of stores you are looking for? Anyway, here are several local large shopping malls for your reference:
Inzone Shopping Mall at No. 66, Luoyuan Street, Lixia District
Guihe Plaza at No. 1, Tianditan Street, Lixia District
Jiahua Plaza at No. 588, Jing Er Lu

I meant to ask if there are any stores in Shandong that sell clothes for larger and taller persons.

I remember there is a store named Pang You (Fat Fellow) store selling large sizes clothes for taller and larger people near East Qingnian Road. You can go for a try.