I think whole Malaysia doesn't sell small size envelope to keep name card, unless u pay extra money to ask name card company to make them for u. Anyway I saw ebay.com has sell them but location is in UK. LOL. If you wish to make small envelope by yourself, the first thing u need to do is calculate the size of envelope u want to make. For my case, here is the size of envelope :
Envelope body size :
12cm width. (It will be 6cm when fold it, so can keep 6cm width of paper in envelope)
8.5cm height.

Envelope head height : 1cm (to close the envelope).
Envelope bottom height : 1cm (to seal up the bottom of envelope).
Envelope left side width : 1cm (to seal up the left side of envelope).

Total width = 12cm + 1cm = 13cm.
Total height : 8.5cm + 1cm + 1cm = 10.5cm.

After know the total size of paper u need, follow the 9 steps below to make an envelop :
Step 1 :
Prepare the tools that u need such as a paper, scissors, glue and pocket-knife as picture below :


Step 2 :
Fold the paper, leave space of 0.9cm on left side as the picture below :


Step 3 :
Fold 0.8cm on each the bottom and upper of paper with ruler as picture below :

Now your paper should look like picture below :


Step 4 :
Fold 0.9cm on left side of paper with ruler as picture below :


Step 5 :
Cut 0.8cm of 4 edges of the paper as picture below :

Now your paper should look like picture below :


Step 6 :
use scissors to cut the paper like picture below :


Step 7 :
Fold the right side and left side of paper and put glue to stick both sides as picture below :


Step 8 :
Put glue on both sides as picture below :


Step 9 :
Fold the paper then cut the head of envelope as picture below :