I wouldn't try creating your own mix unless you've done a lot of research into their nutritional needs - bird mixes aren't going to cut it I'm afraid. You're right to try another mix though as the pellets aren't a suitable feed for hamsters who need a good variety.
As far as I know these are some of the best foods available for dwarfs in the UK (assuming you are!), all of them are better than the old Burgess mix with better variety.
Better if you just have one hamster as it's expensive but it's a really nice mix - suitable for all dwarfs (junior and senior versions are identical)
https://www.rodipet.co.uk/pet-foods/...nior-500g.html
The following have expensive delivery but have bulk options which make them cheaper if you buy more, especially if you have multiple hams (translate page)
https://www.mixerama.de/fertigmischu...en-zauber?c=18
https://www.getzoo.de/getzoo-zwergha...tter-500g.html
This one is also good. I did change my dwarf off it though in favour of the rodipet mix and prefer it.
https://www.zooplus.co.uk/shop/small...d_bunny/620085