Asustek’s prime product, the Eee Pad Transformer slate seems to have reached 400k units a month in shipments, an impressive feat for the Asian company. The slate maker intends to reach a total of 2 million tablet PCs shipped in 2011, that’s very likely to happen, according to sources in the panel supply business.

Asustek’s shipments are expected to grow even more in Q3, according to the sources. The company requested that its touch panel providers keep a steady supply of 400k to 500k units during this quarter, according to the same sources. Internally, the Asian netbook manufacturer has contract orders as high as 4 to 4.5 million units for H2 2011.

The manufacturer that does the assembly for Asus is Pegatron, a name I’ve been hearing a lot recently in relation to Apple and the iPad 3 plus iPhone 5. Pegatron had an impressive June revenue stream, with a 51.7% increase in comparison to the previous one.