'Himalayan Giant' is a particularly large-fruited cultivar of Rubus
procerus and is vegetatively reproduced. It is highly unlikely that
seedlings from this form will be identical to the parent plant and so
seeds cannot be sold as 'Himalayan Giant'. This is why you will not
see them in any seed catalogue. If you want lots of plants of
'Himalayan Giant', you have to raise them from cutttings. (They root
exceptionally easily).