What type of resistance material would be suitable if I want a big resistance around 500k.

the

res_xhigh_po

is around 2KOhm / square, so 500k is not too big. You need 250 squares in series. If you don't need very high precision you can use the smallest width W=0.35. Otherwise go for bigger width like

res_xhigh_po_0p69

or

res_xhigh_po_1p41