The 2001 Fleetwood Mallard 26H travel trailer has a specified weight of 5690-lbs so it is likely to have two 3500-lb-rated axles. You can confirm this axle rating by checking the sticker or plate on the axle tube itself, or it could be included in your owner documentation. The available online data did not include axle capacity for your specific trailer but similar models have this axle capacity.
Leaf springs for 3500-lb axles appear on the linked page. These are offered in several lengths.... view full answer...