spin columns are used for plasmid DNA preparation. these columns are
sold by different companies under different barnd names as kits. The
most popular one is from the company called Qiagen, Valencia, CA. The
main component of the column is SILICA-GEL MEMBRANE. If this component
is available separately, I can make my own column. Please note that it
is NOT just silica gel but SILICA-GEL MEMBRANE. If anybody know a
commericial source for SILICA-GEL MEMBRANE? Please note that I am not
asking the source of spin column made using SILICA-GEL MEMBRANE but the
original source(s) for SILICA-GEL MEMBRANE itself so that I can make
my own  spin columns.

You don't need a silica gel membrane. Just silica gel should do fine.
Way back when I was doing my PhD the Qiagen DNA gel extraction kit was
using silica gel. The one disadvantage of this method was a slight
increase in potential damage to the sticky ends of DNA used for
cloning. If you want a column as in the Q-500/Q-100 plasmid prep kits
you can try the gel as well. Alternatively I would suggest getting
some hydroxyappatite chromatography resin from Bio-Rad or speharose
ion exchange resin would work as well depending upon the pH and salt
content of your washing solutions.