Hello Aanis
GNS3, EVE-NG, as well as Cisco CML/VIRL all have the capability of running the ASA image and emulating a network with an ASA device. Cisco Packet Tracer also has an ASA device, but its capabilities are limited. You can always purchase an ASA as well, you can typically find them relatively cheap on eBay or other online stores.
These options should be more than enough to be able to fulfill most network simulation requirements. If you have any further questions, let us know!
I hope this has been helpful!
Laz