As Sarpedon1978 suggested, why not try a local hobby shop or two that stock Tamiya product?
Racking is generally supplied with a dealers first, initial stock of paint & after that additional section & complete racks can be ordered by them as required, I don't think that it would be too difficult for them to order in what you require.
Part No.;
69037 is the complete rack with 6 shelves, 1 shelf is 9 slot for thinners & aerosols, the remaining 5 are 15 slot for mini acrylics - it's big & weighs in at about 20Kg (over 100Kg when fully loaded!).
69049 is an additional shelf for the above rack, again with 15 slots. This may be more useful than a complete rack & you could in theory get as many or as few shelves as required - these units come with joints which allow them to be stacked on the standard rack or on each other.
69035 for the complete Tamiya fan in you is the branded rack header board.