EVE-NG expects the VMDK to be placed and named precisely.
. Once you have a subscription, you can download the ISO containing all virtual images (vIOS, vIOS-L2, ASAv, etc.). Cisco Service Contract vios-adventerprisek9-m.vmdk.spa.156-2.t download
You will find many websites offering direct .vmdk downloads. While you can find it, downloading from non-Cisco sources: EVE-NG expects the VMDK to be placed and named precisely